ZodTTD is currently working on a SEGA Genesis emulator called Genesis4iPhone. A BETA is now available to testers, with a full release planned in the near future. If you are not a BETA tester and would like to be, the best way to become one is go to ZodTTD.com, register in the Forums, and donate to his project.
To quote: As you can see, things are shaping up nicely so a public release will be on it's way sometime this week. I really appreciate the donations coming in and will be continuing more betas as things progress, not only for Genesis4iPhone but existing and new projects as well.
Updates to PSX4iPhone, gpSPhone, and SNES4iPhone are expected to go into BETA shortly, all adding more performance in landscape mode. PSX4iPhone will be getting much needed attention all around in an upcoming update. SNES4iPhone will also get the addition of sound support. Those who donate will be seeing these releases before they're made public. Check back soon, much more to come!