Tower Defense games

Tower Wars Beta

Desktop tower defense... A CLASSIC!

Honestly?

Plants vs Zombies.

there is Defense Grid, then... the rest :D

Try Defense Grid, as numerous others have said. If you like it, think about supporting the Defense Grid 2 Kickstarter.

Orcs Must Die, Dungeon Defenders - best TD games on steam for me.

I gotta be honest, Plants vs Zombies is one of my favorite TD games, along with Dungeon Defenders and Sanctum.

Toy Soldiers isn't bad if you don't mind it's a terribly shoddy port. Guns of Icarus isn't really a tower defense, but it's pretty close, and I had fun with it.

Oh, and Kongregate.com has a lot of free flash TD games.

Revenge of the titans is a half decent tower defence game.

plants vs zombies FTW :D

Cubemen or Sol Survivor (FTW)

Just a warning: Do not buy Defenders of Ardania. It may look like good on paper, but it is the single worst TD game I've played to date. Terrible !

sol survivor is basically defense grid, but not quite as good. as several others said, defense grid is really really good. it also has a portal themed dlc which is good.

Warcraft 3: RoC/TFT has the best TD maps that any game will ever have.