Today Navizon "virtual GPS" announced support for the iPhone via an application available through Installer.app. Navizon is an interesting concept for getting location information on mobile devices which lack GPS. It does this through a system that Navizon calls "peer-to-peer wireless positioning." Basically the way it works is that people with GPS devices record the location of wifi access points and cell towers. This information is then collated in a database so that when you use your iPhone to connect, it is able to triangulate your location to within a few hundred feet if you're in an area Navizon has data for ("most major metropolitan areas worldwide").
The Navizon for iPhone application is $24.99 and a demo is available (get it through Installer.app or go here) Thanks to everyone who sent this in!