Well,
at least against GBA at the moment, seems that PSP dev kits are not ready yet, so for PSP :)
http://www.tapwave.com
Created by former chaps from Palm. It’s of course based on Palm OS but with specialized APIs for games (3D, …). It has an analog stick, vibration, bluetooth, 480×320 screen, MP3, ATI graphics accelerator… Looks like dream, but has it a chance really ?
I downloaded their SDK but did not have time to play with it :(
Nice piece of hardware anyway !