In one practice match at Western this year our robot first plowed into the wall and kinked the entire frame. We then preceded to slam our knock off bar into the little supporting bar at the corner of the overpass and bent the entire assembly.
Thankfully we had it all repaired by Friday.
Last year on Curie we had one oft he gears at the base of our arm simply snap when we got entangled in another robot. Luckily we had some delrin blocks that essentially locked the rotation in place so we had to turn the robot instead of just rotating the arm. We managed to still do alright without arm rotation.
In 2006 our robot went up the ramp, and then promptly was driven backwards off the ramp and tipped over backwards. We bent the frame, but thankfully it was part of the upper frame and was essentially cosmetic damage, though it looks nasty. It's still bent to this day.