The Claw
Basically it's a USB thing you drape your left hand over with 10 buttons at your fingertips. The buttons can be programmed to generate keystrokes, macros, mouse clicks and scroll wheel movements. Not too useful as-is unless the driver's seat is on the righthand side, but it looks possible to rip it apart and mount the buttons on a custom console. Price is a little high at $70, but I found mine for $15 bucks at a local liquidator.
Inside it there's a small board with a Cypress microcontroller, with ribbon cables running to the switches which are hot-glued into the case. There's an unused expansion header, so it could be possible to add even more switches. Windoze 2K recognizes it as a game controller with up to 32 buttons.
I guess it's not really a "best bet", seeing that it isn't exactly common (didn't find any Ebay), but worth considering if you're looking for a multibutton USB input device.