Tyson/Holyfield was a good one. Tyson *offended* that someone wasn't just gonna lie down in the ring for him without taking a punch. "What? Somebody thinks he's better than me? How dare he!" The fact that the rivalry ends with Holyfield permanently sending Tyson to the LOONY bin makes it substantial.
Burley and Williams deserve a mention, they went 3-3-1. I'll roll with Sweet Pea's picks though, Langford/Wills & Britton/Lewis.
They only fought six times....they should have had a "League" for them with an MVP at the end of the series. Also, the black heavies of the early 1900's had their round robins too.