No Ca$h Gameboy - The best emulator for gameboy. Great sound, joystick compatible, supports Super Gameboy Games and has color (you have to do it yourself). This is the only emulator which can play pokemon.

Gameboy 97 - Good emulator. Not anything special. Can play some games and is joystick compatible.

Virtual Gameboy - Good emulator. High compatiblitily rate. It does not support palette colors.