Once you've looked into the basic towers you might want to start looking at the more advanced ones, the ones you only can get by means of manually building them through tradeskills. These towers are by far the more powerful and useful ones, ranging from special attack towers that will force flying adversaries down to the ground, or force cloaked units to reveal themselves, but they also include some of the "missing" skillbuffing towers (conductors) and Turrets such as the Cold Laser Turrets. Cloud of Polychromatic Nanobots Cloud of Infuriated Nanobots Guardian Conductor of Corruption