thanks for sharing the world of goo game with us. I have never heard of this one. Went to the website and saw that it is 20 dollars but there is a downloadable demo.
All around, probably LGenerals. It is a Panzer General clone.
Also, I have been having a lot of fun with FreedroidRPG lately. As far as FPS, Nexuiz is pretty good, maybe Alien Arena as well.