The following classes have tank specs:
Jedi Knight: Guardian
Jedi Consular: Shadow
Sith Warrior: Juggernaut
Sith Inquisitor: Assassin
Bounty Hunter: Powertech
I'm hoping I got those all correct. The Shadow and Assassin are Cloth classes, but they can still tank as well as the others, they just start a little slower in my opinion. They just rely more on powers to do it, rather then raw armor. All the others wear heavy armor.
You are correct. And the Assassin/Shadow do get a 300% armor bonus to make up for the light armor.