http://www.oxeyegames.com/harvest/
I stumbled upon this game which is kinda like a defense map, except it's funner. It's got lasers, that can link together to make bigger lasers, missile silos that can become cooler missile silos, and a really cool way of constructing your base.
I found it quite fun just playing the demo, but I don't know if I'd go out and get the game. I'm cheap.