Some rofl good combos going on here, ill go for another Robot/Mech load out.
Liberty Prime - Fallout 3: Cannot deny the awesomeness of this Bot, and with an almost seemingly endless supply of Mini-Nukes... Insta-Win.
Starscream - Most Transformers Games Released: Starscream is just, just awesome, hes also a complete Psycho which is always helpful

.
Sovereign - Mass Effect: While not a robot/mech technically it has various characteristics of one, a huge ass ship with its own AI etc, yeh i think this is pretty badass.
Also i have a sort of Fantasy based team aswell.
Sauron - Multiple LOTR Games: Hes just awesome, simple as...
The Lich King Arthas Menethil - I mean this guy just pwns everything, if i have to kill him while raiding in the future i will be highly annoyed (Already know this going to Happen

), gaming will truly loose a bad ass villain.
Mehrunes Dagon - TES Oblivion: The Daedric Prince of Destruction and complete bad assery. Just too cool...