For the PSP, will you be getting games via UMD or mainly through digital downloads off PSN? If the former, PSP-3000. If the latter, PSPGo or spring for a Vita.
For the DS, will you be playing any GBA games or only DS games? If the former, go with a DS Lite. If the latter, try for a 3DS since you'll be able to play games both old and new.