5"x5" is pretty big. Personally, I'd shrink the board and have the motor drivers separate since they are so robot dependent. BUt if you really want to stick one on, have at least 2, along with voltage/current sensing, gate drivers, maybe encoder inputs, and probably 5A or greater, since a 5x5" board is probably a fairly large robot anyways.
If you're talking more of a general "control board" for a robot, then forget about all the really robot specific stuff like the H-bridge (get that separately and properly sized to each robot). Something like buffers for the ADC inputs is a must since every uC ADC I've seen requires really low input impedances. An ICD jack, UART-PC level shifter, I2C line extender/driver (for kicks), CAN bus (for kicks also, but if you build other electronics you might want to base all your other circuits around this bus anyways). Really fancy addons are things like 3-axis accelerometer, 2-axis gyros, configurable lowpass filters for the ADCs, temperature sensor. Don't forget to leave the PWM/output compare pins free for controlling servos as well as the input compare pins for measuring input square waves. Math coprocessor perhaps if your uC is weak in that department. Set-and-forget PWM ICs perhaps.