I'm just a newb and havent been here long enough to remember when Bruce Lovely or Animal Mother were funny so let me give you my votes based on what I've seen in my short time here...
1) Magic Man - Old timer, one of the first on the forums as well as one of the funniest. Who else could have brought Microsoft Paint into Sherdog and make it cool. He should be in the Hall of Fame for his hilarious MsPaint pics alone.
2)Silverwolf - Racist cunt - Yes. However, he was THE most talked about poster on the forum, threads were dedicated to him on a daily basis and whenever he started a thread it always went to at least 7 pages. R.I.P SW
By the way, how come no-one has mentioned Jack Putz? Whether or not he is a hall-of-famer he was a damn funny guy and definitely deserves a mention.