SUPER MUTANT BEHEMOTHS!

There are only 5 super mutant behemoths in the Fallout 3 game. They are found in The Capitol Building, Takoma Industries, Evergreen Mills, GNR Building (Galaxy News Radio), and the Jury Street Metro...
They are the toughest enemies to take down in the game. In every location that you find them in, you'll have some help. Brotherhood of Steel, Talon Company, and turrets that you can activate will make it a lot easier to take down all five. If you do take down all five of them, you will get an achievement called the bigger they are...

Good luck...

BrotherHood of Steel

BrotherHood of Steel Soldier

Enclave

                                                 Enclave Soldier and Enclave Tesla Soldier

RL-3

This is Sergeant RL-3.You can find him  in the Rob-Co Facility parking lot. You must be neutral before you can buy him, and if you are then you can buy him for $1000 I think. He is really strong and a great teammate. If all your partners end up leaving, which it will tell you if it happens, he will be at Canterbury Commons or whatever it's called. He will be in the little field in the middle of the town. If you do get him, BE CAREFUL...