PSP Video 9

PSP Video 9 is a free PSP video conversion and management application. It can convert regular PC video files (avi, mpeg, etc) into PSP video files, as well as manage/copy these PSP video files between your PC and PSP.

As Om Malik points out, not only will this application convert videos into a format that works on the Sony Ericsson P 800/900/910 smart phones.