Finally got around to playing some of the older systems.  It was OK playing it with a keyboard or my MAME controls, but I decided I want to use the original controllers.  Originals that I have are
SNES x 2
NES   x 2
Genesis  x 2 
TG16  x 1
I've purchased USB adapters for the SNES and NES and the NES is close enough to a TG16 controller that I can just use it, not a easily viable option available anyway.
I still need to pick up a N64 and Gamecube controller.  I may never use the Gamecube one since I never played the system, but figured what the hell.  My younger brother loved Mario Kart or Super Smash Bros, so 
I may do that for when he visits.
What USB adapters are you guys using for N64, GC and Genesis ?  I still need to source some GC games, but not in a huge hurry for that.  I believe the Genesis adapter doubles as a Atari one also.