I tend to agree with Chris, go for the PSP if you are into gaming, otherwise get the ipod or some other mp3 player with a lot of space.
I'm planning on getting the PSP myself, and a few extra memory cards. I don't have a large collection of mp3's compared to other people I know, nor do I need them all on one player at the same time.
I also like the PSP because I can play my old games on it by dumping the ROMs and playing them via emulation on the PSP. I will pick up the GTA game that is out but I don't plan on buying any movies cause I wouldn't enjoy them on such a small screen.