I'll second Anderson Power Poles for power, but we've also been using Tyco CPCs (Circular Plastic Connectors) for signal connections with great success. You can see the catalog page here:
http://ca.mouser.com/catalog/catalogcad/646/1576.pdf
In the past we've used DSub connectors, but they required good soldering skills and weren't very forgiving. They can be found cheap though, while the Tycos will cost upwards from $10 for connectors and pins. You'll also want to get their crimping tool ($225).
Our design for the last two years has split the electrical board in two - a signal box (cRio, digital sidecar, etc.), and a power box, each of which can be removed quickly from the robot. The system still needs some work, but it has been a big plus for modularity, and showing students how things should be done in the "real world".