For Nes, and SNes just use the classic controller, it's wireless and is close enough to the real thing.
For the N64 I ended up buying an adapter.
http://www.raphnet-tech.com/products/n64_t...p?category=Kits
It's $20 for just the board, I bought a project box and hacked off the ends to a N64 controller and GC controller. The button mapping works great with several options, one which is good for super smash bros. I mainly got it for playing the the Zelda games for the N64.
Apparently the guy sells just the adapter for $26
http://www.raphnet-tech.com/products/n64_t...x.php?category=
Which is almost as much as the ebay auction, but you can't use Nes/Snes/Sega controllers. If one of those existed when I bought mine, I would have definitely gotten it instead.