Nestopia
Nestopia is a Nintendo NES emulator for Mac OS X. Nestopia is by far the most compatible of any NES emulator for Mac OS X. Using cycle-exact emulation, it is able to run titles that rely on precise timing, and which therefore break under other emulators. It supports five extra sound chips and an astonishing 143 mappers. This accurate emulation comes at a cost; Nestopia requires an 800MHz machine for full speed; but if you have one, this the best available NES emulation for Mac.
http://hanger.org.ua/nestopia/