http://www.retrousb.com/
I've used their kits before ... EXCELLENT for emulation ... you make your old controllers USB2.0, and they use the standard HID-compliant driver, so no software is needed. Just plug into a USB port, launch your favorite emulator, and there you go! They've got options for NES, SNES, Genesis, Saturn, Intellivision, Atari ... all the classics.
However, they aren't wireless. This will be next mod probably, seeing as I have little money and this isn't that expensive.