If you've got an iPad but haven't yet jailbroken it, I don't know what to tell you. What are you thinking?! There's a world outside of Yonkers, my friend. Don't let Apple limit your imagination.
An SNES emulator is a good start — it should run well and of course there is a huge library of games to choose from. Once you're done there, I'd suggest an arcade emulator like MAME — old-school arcade games are great to dip into while waiting for code to compile or a file to upload. The instructions in the video above are helpfully rendered in text over at Lifehacker.