So you might have already seen pokemon tower defense, but those of you who havn't should check it out. If you grew up in the 90's, liked pokemon as a kid, or enjoy tower defence games there isn't a reason to not play this. Its easily the most original TD game I've seen in awhile, allowing you to catch your towers and level them up using xp instead of the normal grind for gold system. You do need money to lvl them up, but it won't take to long to get more than enough cash for that as its not the main priority of the game.
Check out their site sometime http://samdangames.blogspot.com/