Erneto Hoost was always fun to watch, he had great technique for his weight class.
Older Peter Aerts fights were great to watch before he got old, hurt his back and switched his gym. He really could KO people with just about anything and his leg kicking was brutal.
Buakaw is great to watch for his kicking skills.
Ramon Dekkers has to be my favorite though for the combination of skill and heart. He really did throw everything with intent to KO and NEVER fought for a decision. Which, oddly enough cost him some decisions.