Dark Armor - This is a resistance based set that features exotic protections against end drain and psionic attack. The primary weakness is to energy attacks. It has a powerful self heal (dark regen) that requires a to-hit check. This set is very endurance heavy.
Electric Armor - This is an excellent resistance based set with some great utility powers. Lightning reflexes increases the recharge times of all your powers, and power sink is a top notch endurance drain.
Energy Aura - This is a defensive set with a few passive resistances as well. It has interesting utility powers in the form of stealth, energy drain (drains endurance), and possibly the best "Tier 9" defensive power: Overload, which raises max hp as well as all defenses.
Fiery Aura - This resistance based set is the most offensive of the tanker powersets. Burn and Fiery Embrace both augment the tanker's offense. It has a nice self heal, but multiple status protection holes and low overall resistance result in the set being ultimately flawed and weak.
Invulnerability - This is a hybrid resistance and defense based set that specializes in protection against smashing and lethal damage (the two most common damage types).
Stone Armor - The overpowered set of the bunch, this is primarily a defense based set until you get Granite Armor. Granite Armor is basically god mode, and it created a tanker imbalance that has never been resolved.
Super Reflexes - This is a defense based set. The problem with this set is the defenses are not damage type based, which means they do not stack well with other defense bonuses.
Willpower - The newest of the defensive sets, this is a combination of defense, resistance, and regeneration. It is an excellent set - especially when combined with the Fighting Power Pool.