The good folk at Miro (home of the very cool Miro Video Player) have released a neat free and very open source Miro Video Converter program. Shove in any old video file in one end, pull out a mobile phone friendly version at the other. Perfect for carrying around your favourite programs or movies for mobile viewing. Works with iPhones and Android and also supports iPod and PSP. Definitely a download.
Miro Video Converter has presets that will convert video to the correct sizes and formats for popular phones, iPods, and other media players. Just convert your video and copy it to your device.