GT and rivalries is a debatable topic --particularly with the SEC to ACC affiliations:
From the SEC years only UGA has carried over --although Auburn is still a potent rivalry --particularly with GT winning the last two meetings and Auburn choosing to opt out of the third game. It's a shame they don't meet up more often. With exception to three years, GT met Tennessee every year from '54-'87 --but it's been 20 years. Alabama is a similar situation --GT faced them almost annually for 50 years --but the last series between the two ran from '79-'84. Tulane is a former SEC foe whom Tech faced almost annually from the '40s to the early '80s.
In the ACC --although not in the Coastal-- I consider Clemson our biggest rival. This is based upon longevity --with exception to the late-'70s/early-'80s GT has faced them every year since the early '60's, longevity in the series itself as Clemson holds a 13-12 advantage since '83 --with 13 of 18 games decided by <TD, and proximity figures in as well. FSU was well on it's way to becoming a rivalry game --with five good games from '99-'03-- but division alognment has killed that.
The Coastal Division teams are/or will become rivals. UVA is certainly a rival to me --Miami is becoming one, VT is not yet, GT has faced UNC every year since joining the ACC (UNC leads 12-14-1) --but it doesn't feel like a rivalry. Duke for practical purposes should be a rivalry --GT has played them every year since '33, it's always been a home-n-home series, GT leads overall 44-30-1 --but with GT owning a recent 16 out of 18 edge and, well, Duke being Duke, it's not looked at as a rivalry.
My top five rivalries:
*UGA
*Clemson
*Auburn
*Virginia
*Miami