Asteroids tower defence. Build your probes to defend the base from asteroids. Original game with nice towers and upgrades. And also a small funny story attached.

Based on the real life human defense system. Defend against evil bacteria and viruses. It's possible to build a maze like DesktopTD. The game and towers are pretty complex but once you've figure it...

Frontline Tower Defence is all about preventing bugs from reaching the other side. Only classic mode available but thats the most fun anyway. Typical tower-maze game if you know what I mean...

Defend your girlfriend against lines of creeps, game from Addicting Games. Place your towers smart in a well balanced game against some evil looking holy pig.

SNAFU TD is a military themed tower defense game. It features multiple missions with ingame achievements. The different maps are challenging and the game looks good.

Second part of the Protector series. Again the 3D isometric perspective to the game and and fantasy world as theme, go through the map for a lot of missions.