has all the emulators you would ever need, but they don't host or link to rom downloads. For NES, Nestopia and FCEUltra are the best. ZSNES is the best SNES emulator, though there are a few others out there with good functionality.
As far as roms go, well, do some searching (I'm not about to link what basically amounts to a pirating website here). It's a pretty big gray area as to the legality of it. Getting stuff that wasn't ever released in your region is probably fine, but I would make an effort to acquire the actual carts of games that really are/were available in your region.
For old PC games, try http://www.gog.com