Y'all forget all about UGA-UF! It's kind of taken a back seat to Florida's other rivalries in the past few years, but it is very heated. We even play it in a nuetral place -- Jacksonville, FL. The stadium is divided in half, much like ktsnake mentioned above with the Texas vs. Oklahoma game. I have a feeling that the game this year will have more significance than those in the past few years...
We have a lot of rivalries, but I think most UGA fans would agree that Georgia Tech, Florida and Auburn are our most hated.
UGA vs. AU is the south's oldest rivalry.