Yieldex, a service that forecasts online ad inventories and aids publishers in making the system work smoothly, took the top prize in Amazon's second annual Web Services Start-Up Challenge.

That prize is more than just a loving cup; Yieldex will get $50,000 cash, $50,000 in Amazon Web Services credits, and maybe -- maybe! -- an investment offer from The House That Bezos Built.

Online advertising may seem like just more screen clutter to some (of our more jaded) readers, but the process of getting ads on your screen is a wildly complex one, with plenty of moving parts and a few loose screws. To tackle the problems of figuring out what spaces are available, which companies need space, when the ads should appear, and how to get the appropriate files to the right places at the right times -- not to mention the crucial step of making such everyone's paid -- Yieldex developed the DynamicIQ platform, which sits atop AWS.

Fancy stuff, and the use of cloud computing to handle the guts of the system (the "operations that do not differentiate us from our competitors," as Yieldex VP of Engineering John Barr puts it) frees Yieldex's team to do their thing.

But the other six services that made the finalist round aren't exactly blowing smoke up in the cloud either:

• Encoding.com bring accessible, scalable video encoding to the masses via SaaS. (Last year's AWS Challenge winner, Ooyala, is also a video-oriented firm.)
• Knewton turns test prep on its ear by making test-worthy content granular, tagging those grains, and reassembling them on the fly in its adaptive-learning engine.
• MedCommons lets patients manage their health records and other information.
• Sonian does a hosted e-mail archiving service.
• Pixily provides interactive document management, whipping both electronic and paper documents into usable form.
• And Zephyr's Test Management Platform puts software QA testing departments into the cloud for, ironically, more management visibility into the process.

The competition itself was exciting stuff, as described by Yieldex CEO Tom Shields in an ebullient blog post ("We won! Out of nearly 1000 startups who applied, we won!").

The seven finalists gathered in Seattle and, one by one, made their case to a panel of senior Amazon executives. After that, the companies made the rounds of a "VC speed-dating" meetup, with five venture-cap firms getting the 10-minute pitch from each finalist. VC being what it is, of course, it's possible that this portion of the day will pan out for many of the finalists. The day ended with a reception, the announcement of the winning entry, some spontaneous shouting and fist-pumping, and a thwack of an old rackmount server with a golden hammer.