The first great wireless console gamepad was the GameCube’s WaveBird. I’ve still got mine, and I break it out occasionally and it still feels as great as ever. To try and replicate that with the older systems you’ve either had to use the wireless controllers that came out then, which were all pretty bad, or buy one of the new knockoff systems that comes with wireless controllers.
It looks like there’s another option though, for those of us who are a bit more hardware-hacking inclined, thanks to a great post by user micro over at nfggames.com. Seems he’s found a very nice (and importantly cheap) wireless transceiver that will work great for all of the old systems. He’s even put one into an N64 rumble pad. Head on over to check out his awesome work, and see if you feel like taking it on.