Long answer,
DS Lite for unique games, Nin franchises, and HUGE library of GBA games
PSP
for media, great looking PSP games, internet/email (I assume this has been implemented by now), homebrew, and great emus. Also, cheaper handheld + cheaper games overall means better savings, not that PSP is breaking the bank, but it's higher price is still significant
However, get a standalone MP3 player for high capacity music, PVP for DVDs if ya got alot of 'em, and a PDA if u plan to do alot of 'heavy' internet activities. I find it most ironic how many have spent all that $$ for a great screen and graphics, only to end up playing the likes of Gen, NES, and SNES games on there, with n64 and ps1 on occassion