That’s the basic premise behind Metamarkets, a 2-year old startup that just raised another $6 million.

This was an inside round, with most of the folks who invested $2.5 million a year ago re-upping: Roger Ehrenberg’s IA Ventures led the round, and previous investors including Village Ventures, True Ventures, Omnicom vet Jerry Neumann and Foursquare CEO Dennis Crowley chipped in.

CEO David Soloff says Metamarkets now has 3 paying clients, and is recording between 3 and 5 billion “events” — ad impressions bought and sold – per day. Metamarkets stores and analyzes all of that data — it’s up to 500 terabytes so far — and the publishers are supposed to use it to help them figure out how much to price their inventory in real-time. It’s also supposed to let them predict what kind of business they’ll be able to do in the future.

Originally, the company thought it would also compile that data to create the equivalent of stock index, which buyers and sellers could use to gauge the state of the ad market.

The idea: If  you were buying inventory from, say, Google, it’d be good to know how the rest of the market was performing. But for now Soloff says they’re busy with the proprietary products they’re selling directly to ad sellers.

Metamarkets will use the money to build out its 14-person engineering team. But the company’s existing workforce is already doing something right: I’m told that Twitter, among other potential acquirers, did some tire-kicking before the company closed this round. Soloff wouldn’t comment on that line of questioning; I’ve asked Twitter but don’t expect to hear much from them, either.

Of course it could be, which is why lots of companies are trying to build businesses around the idea (while trying to avoid privacy landmines). Here’s another one: PlaceIQ, a Boulder, Colorado-based start-up that promises to turn “unstructured disparate sources of geodata into actionable business intelligence.”

Co-founders Duncan McCall and Steve Milton formed the company last year and have a small team with a low profile, but they’ve been able to round up $1 million in funding from some interesting investors: Roger Ehrenberg’s IA Ventures, Howard Lindzon’s Social Leverage, hedge fund star Jim Pallota, Jerry Neumann and Stuart Davidson are all in.

So is kbs+p Ventures, the new investment arm of ad agency Kirshenbaum Bond Senecal & Partners, which has begun making bets on start-ups with potential for marketers. This is kbs+p’s second investment, and I gather we’ll see more soon.

Here’s Sulia, which is dedicated to finding and sorting the most relevant Twitter users into related groups, so you can follow them.

The New York-based company has raised $3.5 million in a round led by FirstMark Capital. Other investors, who had previously put in $1 million, include Bo Peabody’s Village Ventures, Roger Ehrenberg’s IA Ventures, Chris Dixon’s Founder Collective and Ron Conway’s SV Angels.

If Sulia sounds vaguely like TLists, which did something similar, there’s a good reason for that. It’s the same company, rebranded and tilted slightly–can’t call this one a pivot.

The main difference is that while TLists was primarily supposed to be a tool for Web publishers and Twitter clients–it already works with TweetDeck, Flipboard and Mashable–Sulia is supposed to do that and provide a destination Web site. That is, it is becoming a publisher itself.

How will Sulia make money? The same way Twitter wants to: Act like a media company, and sell ads against the eyeballs it collects.

CEO and founder Jonathan Glick knows that world pretty well, given a work history that includes stints at iVillage and the New York Times. Prior to the start-up, he was director of research at Gerson Lehrman Group, which is both the subject of legal scrutiny and the world’s largest “expert network.”

At one point this summer, when the company was still called TLists, the start-up had a working relationship with Twitter, where it powered a grouping feature on the service’s profile pages.

From what I can tell, that feature disappeared with Twitter’s redesign, but I’m told the companies are still working together and may have something to show off within a few weeks.

The New York start-up isn’t getting rid of captchas, but it does promise to make them more tolerable: It says it can swap out the random, hard-to-read text with clear, concise English. And while it’s at it, it says it can turn captchas into revenue generators for publishers, by transforming them into ad units.

It’s a super-simple pitch, and if you see the ad units Solve Media is selling, it gets even easier to understand. So click the image to enlarge:

How can Solve’s easy-to-read English text defeat the bots and other evildoers that captchas are supposed to foil with their jabberwocky? Got me. I’ve got no way of verifying its claims, either.

But assuming it does work, CEO Ari Jacoby has an interesting product on his hands. He’s pitching it specifically to display advertisers and big brands that put a lot of money into TV spots but have a hard time doing much with click-per-action schemes offered by Google’s (GOOG) AdWords and others.

The idea is that Jacoby’s ads require users to engage with them, by typing in the names of brands and products. But they don’t do anything beyond that–they don’t trigger a video, or take you to another Web site or anything else. It’s sort of like sitting on your couch and uttering “Outback” every time a Subaru spot comes on.

Jacoby claims his “type-in” ads will increase Web surfers’ recall of the ads, for the same reason that writing anything down makes it easier to remember.

That’s much more valuable than taking users to a branded minisite, he argues. “If we can deliver the cognitive payload up front, then we don’t need to deliver the users to a site that they don’t really want to go to anyway.”

And Jacoby thinks advertisers will pay up for the privilege, in the range of 25 cents to 50 cents each time a surfer types in a brand or product. He’ll split revenue 50/50 with publishers.

Playing along so far: Advertisers including Microsoft (MSFT), GE’s (GE) Universal Pictures and Toyota (TM), and publishers including Meredith (MDP), Tribune and AOL (AOL).

AOL is also an investor in the company (previously named AdCopy), via its AOL Ventures arm. Other investors, who have collectively put something like $6 million into the company, include First Round Capital, New Atlantic Ventures and angels like Chris Dixon, Roger Ehrenberg, Aydin Senkut and Shervin Pishevar.

Solve Media from Solve Media on Vimeo.

So here’s a company that wants a piece of that: TicketFly, a New York-based start-up that just raised a $2 million Series A round led by High Peaks Venture Partners and Contour Venture Partners. The company had previously raised $1 million in convertible debt last year, via angels Howard Lindzon and Roger Ehrenberg, among others.

If TicketFly works, there’s a good chance you won’t ever know about it, because it’s a B2B business: Consumers fund the operation via surcharges on their tickets, but the real customers are the concert venues, which strike exclusive deals with ticketing companies.

So most of the features are designed with the venues and promoters in mind. TicketFly says it can help with Web site design and management, promoting shows on Twitter and Facebook, tracking sales data in real time, etc.

All of this sounds like fairly straightforward stuff, but the ticketing business is an old, archaic one. And Ticketmaster, the industry’s eight million-pound gorilla, now owned by Live Nation (LYV), is particularly slow-moving when it comes to all things tech. So some of this really will feel fresh for the concert guys.

More interesting are TicketFly’s plans, which involve giving venues the chance to sell tickets using the same dynamic pricing/yield management techniques hotels and airlines use: That is, prices for hot shows may shoot up, and if you want to see a band no one else wants to see, you may end up paying very little.

TicketFly has about 50 venues signed up so far, and most are fairly intimate places like Maxwell’s in Hoboken, N.J., or the Triple Rock Social Club in Minneapolis–the kinds of of places where you could see Nirvana before Nirvana became Nirvana.

They’re also the kinds of places that used be served by TicketWeb, another Web-based upstart that Ticketmaster acquired a few years back. No coincidence: TicketFly co-founder Andrew Dreskin used to run that company.

Here’s a little wayback machine: Nirvana at Maxwell’s in 1989. Audio and video quality is about as rough as you’d imagine:

Green has rounded up about $2.5 million in financing for the Ventura, Calif.-based company. Founder Collective and Roger Ehrenberg’s IA Ventures led the company’s first round; angel investors include Josh Stylman, a co-founder of Interpublic’s Reprise Media, and Omnicom vet Jerry Neumann.

The Trade Desk is one of a growing number of “demand-side platforms” that are supposed to help ad buyers grab inventory from exchanges like AdECN and Google’s AdX. The idea is that the exchanges, which churn through a staggering number of ad impressions at very fast speeds, require ad buyers to use specialized software and services if they want to make the most of them.

It’s still unclear if ad buyers and publishers will embrace the exchanges. But investors love the notion, as well as the idea that the big ad holding companies, or perhaps even Google (GOOG), will want to buy a DSP or three. So the market for this stuff is beginning to get a bit frothy.

That’s one of the reasons Green is reluctant to use the word DSP to describe his seven-man company. But given that his team is still building the product and that he doesn’t want to talk about it until it’s up and running, we’ll have to use that term for now. You can get just a bit more info here.

Newest example: StockTwits, a Twitter-based bulletin board/chat room for individual investors. The company has raised more than $800,000 from a big group of angels that includes Roger Ehrenberg and Howard Lindzon (disclosure: Ehrenberg and Lindzon invested in my previous employer). Ehrenberg has provided a long list of investors at his blog; other notable names include Betaworks, the New York-based start-up investment company, and Todd Stottlemyre, the former Toronto Blue Jays pitcher turned investor and Twitterer.

The idea is fairly simple: Users toss off quick thoughts about trades, companies, markets, etc., using “$” or “$$” signs to identify their messages as StockTwits. The site compiles and sorts them, and will eventually start ranking users based on their following, track record, etc. The service is free, but will try to upsell users with premium products like research, etc.

You could do all this without Twitter, if you wanted to. But the service is perfect for the rapid-fire bursts of text/thought that a certain breed of investor treasures. And, of course, Twitter does all the heavy lifting for free, so why not build a business off its back?

Twitter isn’t the only Web 2.0 business to let other people build services based on its API, of course. It’s standard practice for everyone from Google (GOOG) to Facebook. But usually those businesses benefit because users end up more closely tied to their core businesses, which… is a business of some sort. Since Twitter has yet to actually generate any business, it’s just a giveaway.

That could change sooner than later: Twitter is hiring a “Business Product Manager” who is supposed to “lead the definition and execution of the products and features that will lead to monetization of the Twitter platform.” Perhaps step one will be a phone call to StockTwits and the other members of the Twitter ecosystem.