Football: I'm going old school here - Sonny Jurgenson, how could you not like a beer bellyed redhead who could throw the ball 80 yards on target. The man has never gotten his due when people talk about the best QB's of all time. Honorable mention - Earl Campbell, which someone mentioned earlier and I completely agree. His short career was marked with brilliance. Talk about someone blazing fast who simply looked for people to run over and through.
Baseball: Kirby Puckett - he could light up a room with his smile and personality, he could hit for average and power, he carried the MN Twins to two World series victories, and long before Tori Hunter starting stealing home runs in the metrodome with his fielding gems, Kirby was doing it. It was a very sad day for baseball when he had to retire in his prime because of glaucoma in his eye.
Basketball: Dr. J - Julius Erving. He was slamming, flying, and doing serious air time long before the Jordons, Bryant, et al were doing it. He was the trend-setter for today's basketball stylists. Plus he was one classy dude. Love ya, Dr. J.
Tennis: I rarely watch it, but Anna Kornakova (sp?). Do I really have to tell you why??????