You got some really big motors you want to control? Take a look at the Sabertooth dual 25A motor driver, able to supply 25A each to two motors, at up to 30V. It's a brute, but it's smart enough to talk in many ways!
This is the bigger brother to the Sabertooth 2X10, which itself is a very nice, flexible dual-motor controller. But this is a monster, able to power that 100lb combat robot, or regular (non-life-threatening) 300lb robot with authority!
The Sabertooth 2X25 is spec'd out to drive 2 DC brushed motors to up to 25A (50A short term) at up to 30 VDC. And like the rest of the Sabertooth series, it has overcurrent and thermal protection that keeps it safe from excessive loads (like stalls, or really oversized motors).
The Sabertooth 2X25 understands input via several methods, being:
Did you know this Sabertooth has "synchronous regenerative motor driving"? This means it redirects power generated by coasting or braking motors back to the battery, which extends battery life. A very cool feature, which makes great use of power that would otherwise be used up as heat.
The Sabertooth also has a built-in 5V battery eliminator circuit (BEC) that can supply power to a microcontroller or R/C receiver.
Whatever you do, don't use a cheap AC/DC wall-wart as the power supply for this motor controller. If you must, at least wire in a suitably large battery in parallel with the power supply. 25 amperes of current is a huge amount of power to draw from a wall-adapter!
In short, here's what it can do: