Controller secondaries provide a variety of different support powers. They are similar to defender primaries but tend to have slightly lower effect values.
Empathy - This is the primary healing type set. It also has one of the best buffs in the entire game: Fortitude. The regeneration and recovery auras buff the whole group giving them excellent health and endurance recovery rates.
Force Field - This set focusses on protecting the entire team with defense based shields. This set also provides status protection to the controller and the controller's team.
Kinetics - This is the most purely offensive based set for the controller. It drains foes of their ability to deal damage while massively buffing the controller and its team. It can also boost speed, endurance regeneration, jump height, and more.
Radiation Emission - This is the best debuffing set in the game. Radiation can debuff regeneration, defense, to-hit, and damage resistance. When you can debuff these things, Arch Villains become significantly easier. A lot of end game content practically requires a radiation emission team member.
Sonic Resonance - This set is similar to force field but the "bubbles" protect via damage resistance rather than defense. This set also provides status protection to the controller and the controller's team.
Storm Summoning - This offensive/PvP based set is popular among soloists and PvPers but it is not group friendly.
Thermal Radiation - This was originally a villain corruptor set but was recently given to controllers. It is a hybrid of sonic resonance and empathy/
Trick Arrow - This is the most unique of the controller sets. It has a variety of debuffs that take a good deal of practice to use effectively.