Syn-z has released a new version of whats probably the best Genesis emulator for the PSP at this time, heres whats new: (via Translation by b8a)
Ver 1.40
* Added wireless multiplayer functionailty.
(for details on connecting, etc... refer to adhoc.txt(adhoc_eng.txt).)
* The simple multiplayer functionality has been removed.
* Fixed it so that the speed is adjusted when Frame Skip was set to 0.
* Fixed the problem with turbo not working when Frame Skip was set to 0.
* Fixed it so that when recovering after sleep during a game it returns to the menu.
* Added the ability to exit (return to the PSP menu) from the menu screen.
(it's "analog <- +START" when in the menu scree