My favorite was E-313 Heavy Repeating Disruptor
, it could be bough for 11k (I think) credits on Tatooine in Speciality Shop.
That shop was really useful when I arrived at Tatooine for the first time.
This is the coolest one I've found so far. (at least, in my opinion) I still used it at 50 until I got my PvP one, which doesn't look as cool.