Cool project. Here's what I've found.
Since you're packing around a whole computer, you're probably going to want motors along the lines of what's used in FIRST (correct me if I'm wrong), meaning that a lot of the low-current motor controllers would fizzle and die. So from there, really the best option that I know of is going with the
IFI Victor controllers. Since they're controlled with servo PWM signals, you need a controller board like you said. There's a bunch of different options for this, most have 8 or 16 outputs, a couple I've found are:
Pololu USB 16-Servo Controller
Super Servo Controller
There's also several guides if you want to DIY (like
this one)
For more just google serial servo controller
Good luck!
--Ryan