Just reposting something I shared a couple of weeks ago (be advised a couple may no longer be available at MSRP):

I've gone overboard with my USB controllers, from RetroFlag for SNES, Hyperkin for Genesis, Hori for TurboGrafx, the PS Classic controller for PSX, Hyperkin for Atari, and a RetroUSB NES adapter for my original controller (there aren't many good 2 button NES style controller) ... and a crap ton more, ha.