In addition to the addicting Desktop Tower Defense*, found a couple of interesting tower defense games. Which of course you won’t play during work because you’re bored or lazy.
Bloons Tower Defense 3 is a sweet upgrade over the second one. Dart-throwing monkeys, Spike-o-pults, and Pineapples are all part of your arsenal to pop “bloons” (balloons) before they get to the other side.
Gemcraft’s tone is more serious; you create gems to put in towers which zap the monsters created by some evil wizard. It looks to be a LONG game to actually finish and I probably won’t bother. You might though.
I like the monkey game better.