[euhlmann]

Lots of teams use the Raspberry Pi or an Nvidia Jetson board.
The Pi is relatively easy to program on (in python, and it's easy to install the OpenCV bindings for python).
I don't have any experience with the Jetson but I assume it's more difficult to use than the Pi. However, the Jetson is also vastly more powerful.

The third option is an Android phone. A handful of teams used one last season. The advantage is that you get a high quality camera and a powerful processor in a single package. It's also easy to use OpenCV in Java. The caveat is that Android OpenCV doesn't use the GPU by default -- to enable it you need an Android with OpenCL support, and you need to use the T-API in native code (which is more difficult)