handbrake is the one i've had the best results with.

Mike - it converts ("rips") the DVD to AVI, MKV, etc. It can pretty much convert any movie format (avi, iso, vob) to any other format. There's a setting in there for PSP I believe, which would be what you need. I rip DVDs we own to our Media Center PC to watch on my xbox with XBMC. I do this overnight, since it does take a while.

I suggest ANYDVD as most of the newer DVDs have a form of copy protection.

(Note - i'm just talking about movies you already own. I'm not telling you to steal movies.