Here is my list

The original Hitman, Hearns
Monzon
Hagler
Felix Tito Trinidad (All time fav right here)
Miguel Cotto
Wilfredo Gomez
Juan "Baby Bull" Diaz
Johny Tapia (Gotta love "Me vida Loca")
Angel Manfredy (Same reason as the second poster)
Young Mike Tyson

All these guys have one thing in common. They did'nt puzzyfoot around with you. They go into the ring to do one thing and one thing only, kick your ass. No ifs, no buts, these guys were going in to beat the living crap out of you and if you were'nt 100% ready (most times despite of the fact) you were going to end up in your back.