A lot of the ones I was going to mention already have been - Whew, Caesar's Challenge, etc. I'd probably include Battlestars and Celebrity Sweepstakes on the list. Despite close to a three-year run, I don't think too many people remember the latter today except for us.
My top choice would be the 1976 Break the Bank. I realize it was kind of a Squares ripoff, but I always thought it was a high-quality and kind of interesting game. I love the set! I don't think it got a fair shake - the ratings were strong through the 15-week network run (I believe somebody posted ratings from June 1976 at one time and they were still high), but it was cancelled in favor of expanding soap operas. Why they couldn't have changed the timeslot and held off the debut of the (strange) Hot Seat instead, we'll never know.
When the show was in the "checkerboard" syndicated slots in the '76-77 season, it was up against shows like Hollywood Squares, Match Game PM, $25,000 Pyramid and the nighttime Price is Right in many cities, all of which had established audiences. The next fall Jack was more interested in the revival of Joker's Wild than this.
GSN only gave us a third of the run a couple of decades ago but very little of this show has popped up elsewhere in all that time.