NES,SNES,NDS,GBC,GBA,Sega CD/Genesis,MAME - Emulators and ROM Packs

NES
SNES
Nintendo DS
GBC
GBA
Sega CD
Sega Genesis
Multiple Arcade Machine Emulator (MAME)

Each console has the emulator in their respective folder and each has full ROM packs including All US games and some other regions as well.

Just run the emulator for the console you want to play and browse for the rom in the folder for that console.