For controllers, I usually hate to, especially for the Gamecube, nothing has ever been able to recreate the quality of the OG's there.
For the first Xbox, I have found pretty much any controller to be perfectly serviceable. Every other type of accessory besides controllers I love third party. Link cables, memory cards, and anything else I think is just great to have a cheap, out of the box version of. Tomee, PowerA, and Hori all have my heart.
What I desperately want is for any 3rd party company to step up and reproduce the Gamecube LAN adapter that slots under the console. It still costs around $99 on eBay and although I know there's very little market for the 2 games that it supports, I really want to see a cheap version of it so that I can play kirby airride and mariokart double dash with all of my cousins.