PSPgo Video 9

The software can convert all types of video files (avi, divx, xvid, flv, x264, vob, mpeg, DVD's, YouTube, etc.) into the proper video formats (MPEG-4, H.264) that play on the PSP Go.

It is available for Windows and Mac.
PSP Go Video 9 is a free PSP Go video converter that converts video files, YouTube videos, movies and DVD's so you can play them on your PSP Go.