I like subtle references to previous episodes. In last night's show, "The Handicapped Spot", I noticed two.
The first was when they were driving through the mall parking lot and Kramer said "Don't forget where you parked the car". That one was a not so subtle reference to the epsiode a while ago which also took place in a (the?) mall parking lot.
A more subtle one last night was when George was in his mother's apartment. It was at the end of a scene and there in the background while other's were talking was George sitting on the couch, reading none other then Glamour. The same magazine that got him so excited in the contest. I was waiting for his mother to say something like "Oh God, George, stop reading that filth!" But of course subltity is better.
I imagine there are tons of these references which fly by unnoticed.