I bought some arcade-quality joysticks and buttons for use in my cabinet:
They are made by Happ Controls, and are great quality. I would suggest buying them from a reseller like Tornado Terry’s or another eBay store for the best price.
My control panel will have two joysticks, with six buttons for each. The interface to the computer is handled by hacking a keyboard, or buying a specialized control board. I went with a board I got pretty cheap on eBay, (Tokn-10) though I don’t recommend it because there are much better ones out there that I’ll discuss in a later post.