Gatling Tower:
Great tower for quickly constructing defenses. Dirt cheap and surprisingly powerful. What this tower lacks in range it makes up for in its low price and damage.
Goo Tower:
This tower is a must for those sticky situations when you need to slow a fieldrunner down. This tower reduces enemy movement rate and the effect increases with each upgrade.
Missile Tower:
A great defense against air units. The missile tower's explosive damage hits multiple targets at once. This tower has a very long range.
Lightning Tower:
An ultimate weapon of devastation. This tower fires a single bolt of lightning that incinerates most fieldrunners in seconds.