If you want homebrew, just go out and get a GP2X
However, bear in mind that for emulation the system(s) you want may not be very good yet.
What I can tell you though is that Genesis = near perfect, as is old MAME (.34 ish). Also, there's great homebrew games already on this system, with noiz2sa as a good example.
In time though, it looks like all systems up to SNES power will be near perfect, and PSX emulation is a very real possibility.
Also, movies look DAMNNN nice on the thing. I mean, holy shit shiny nice...
EDIT: Oh yeah, it's all also much cheaper too (memory card, system), although I recommend an alternate carrying case, 4+ rechargable batteries with a SLOW charger (6+ hour charger, 2500 mAH AA energizer is fine) and a SD card reader (heard DS carrying cases work well)