/ Emulation \
- Emulators -

Gameboy Emulators

Gameboy 97- This one is probably one of the best aside from maybe Virtual Gameboy(Costs money for Virtual Gameboy though). But this is all you will need. It has sound and different things.

Snes Emulators

Snes9X and Snes97- While snes97 is for windows it has kinda lagged behind the pack. But the same creators have been working on the new Snes9X which was formerly known as Snes96. Snes9x is one of the best emulators for the snes, advanced features like sound, saving, mode 7, and many other things.
Zsnes- This is the second best emulator for the snes. I use this one currently over Snes9x..because the sound is better, it seems. It is also pretty fast too and plays Yoshi's Island (Super FX Support).

Nintendo Emulators

NESticle- It appears that their site is down for now...but this is the greatest nes emulator it runs almost perfect!! Sound, and all. Even advanced features like auto save anywhere, net play, record movies, record waves, and much more! The BEST!