One of the oldest but best consoles has some great emulators released for it:

Nes Emulators
AminNes
DSP
FCEuMM
Fceux
FCE Ultra
FireNes
JNes
Macfceu
MyNes
Nemulator
Nintendulator
Pasofami
Retrocopy
RockNes
Smartgear
Ubernes2010