wow, really?! Not one mention of .emu emulators?
Robert Broglia has a series of emulators for iOS devices. He's pretty much covered all the pre-3D systems, at least the more well known ones. Pretty much every one works very good, smooth, stable, etc. the GUI is done rather well: simplistic in design. Works well for touch screens.
Most of his emulators cost money, and personally I think are an extra dollar or two high, but I've not yet once regretted any purchases from him. His emulators also support a bevy of features: controller support, cheats, save states, among others I can't think of at the moment lol.
His website:
Www.explusalpha.com
But you can find his emulators on Cydia.
No offense to Zodttd, but his emulators pale in comparison, and I hope he sparks a renewed interest in development for his emulators to improve them. In the meantime, I cross my fingers every time Robert announces a new .EMU emulator, in hopes it will be for a new system that I want to play on my iDevice.
Also, while most of his emulators cost money, his snes9xex emulator is free, so find it on Cydia and download it, and give it a try. You can expect pretty much the same experience with his other emulators.
Finally, yeah emulation on iOS sucks. There is a severe lack of 3D emulated systems on iOS, and I would like to see a surge of actual, decent emulators for newer systems (n64, psx, etc) at the moment, Zodttd's version of said emulators are not up to snuff for my tastes.