Robocode is a very interesting game programming concept that I came across recently. The basic idea is to develop an algorithm for controlling a robot tank that will participate in a battle with other similar robots in a battleground.I got introduced to this through an ACM programming competition in my university.
Robocode Simulator
The impressive thing about Robocode is that we need not bother about the visual effects. How to draw the robot is not our concern. The Robocode simulator takes care of that. The battle is, I think, based on discrete event simulation.
Robot
Now coming to the interesting part. A robot is basically a tank with a body, a gun and a radar. Each component can move by itself, either independantly or relative to the component below (Radar is on top of the gun which is on top of the tank body). We need to define how the robot moves and how it handles different situations. What happens if the robot hits a wall (end of the battle ground)? What happens if the robot is hit by a bullet from another bot? The way each person handles these situations is what differentiates a simple robot from an exceptional one.
I am developing a bot myself (Mercury). It is ready for battle at the amateur level. It fights decently well with the sample bots but fails *miserably* against the pros 
. Please contact me if you want to discuss about the algorithm I have used or anything else regarding my bot.
I can rant on and on about what Robocode is all about. But I dont want to duplicate (or give false information!) about the details. I think the wise thing to do here is to give links to some good sites on Robocode. Which is what I have done below. Have Fun!!
Links