[Alan Anderson]

The Cypress "FirstTouch" board accepts switch inputs and analog voltage inputs and a number of other controls. Support for it is built in to the Driver Station program. The board is a little expensive if you don't already have one, and connecting to it can be more of a hassle than it needs to be unless you buy a purpose-built carrier board.

There's a "Custom Control Interface" board from eStop Robotics that takes switches and pots and emulates a vanilla USB joystick. It's an off-the-shelf solution, developed specifically for what you want.

Some teams have programmed a "Teensy" board to do the same sort of joystick emulation. It's cheaper than the CCI.