You can purchase a Windows Phone 7.5-based HTC Titan for one cent today only, online only, from AT&T Wireless. This is the largest Windows Phone handset and the one, I believe, with the best camera. Originally, I had expected to see this phone appear as part of AT&T's Black Friday sale. But it's available (for now) at last.
The purchase requires a minimum data service starting at $15 per month with 2 year contract and new activation (normally; activation fees are apparently waived today). Stepping through the wizard, it appears you can also get the deal by adding a new line and using this as a second phone (which I'm thinking about).
Thanks to Jeff F. for the tip. And to John T. for noting that a bunch of other Windows Phone are also available for one penny, again, today only.