Robot Contests and Ideas

http://www.usfirst.org/

VEX Competion
http://robotevents.com/robot-competitions/vex-robotics-competition/colorado-vex-tournament.html

Robot Laser Tag
http://www.nerdvest.com/robotics/RoboTag/index.html

Robot Freeze Tag
http://www.math.northwestern.edu/~wphooper/fun/rft/about.html

Lots of ideas of sensors, controllers, and such
http://www.arduino.cc/playground/Main/InterfacingWithHardware