You can go to emusanet.com. They have all the best emulators and tons of versions of the best games out there, up to the end of the 16-32 bit era. And man, you should see all the Super Mario Bros. hacks they have!
Super Bald Bros., Disembeveled Mario, Super Mario Bros. 4, and even a wacked version of Super Mario 2 that stars robots!
I am FLUDD, the Flash Liquidizing Ultra Dousing Device. I hope to be of assistance.