A quick version of a golem game i made. Updated- The tanks are a lot smarter (and a lot deadlier now).
Click on unit buttons to spend money on that unit. Every 20 seconds, the unit spawn comes around and all the unit types you've purchased will spawn. They are cumulative, which means once you purchase a unit it will spawn each and every time.
The game uses the spritlib gpl http://www.flyingyogi.com/fun/spritelib.html free sprite sheets by Ari Feldman.