I hope I'm doing this proper to the BCS forum. If not, then I submit myself to the mercy of the mods.
Creeper World by SavaTheAggie, on Flickr
My new favorite time waster - Creeper World. It's a tower defense game, but it isn't at the same time. It's one of those just go play it and see for yourself type things. If you like strategy games, I think you're about to lose a few minutes of your life.
The "demo" with 6 levels can be found here: http://www.addictinggames.com/creeperworld.html
I liked it so much I paid the $10 for the full version which is claimed to have 1 million levels (I've cleared some 20 so far). It also has the distinction of the very first game I've ever bought on-line (as in, paid my money and was given a link to a file), which if you know me speaks very highly of this game.