What Super Bowl champions have made it back to the Super Bowl the following year and failed to defend their title?

Most of them. Out of 42 chances to defend their title, only 8 teams did and only 3 teams tried and failed. Although the Packers, Dolphins, 49'ers, Cowboys, Broncos, Patriots and Steelers (twice) had consecutive victories, none even got a chance for a third. Only 3 times did a team win one Super Bowl, then lose the next one. * The Dallas Cowboys won Super Bowl XII, then lost Super Bowl XIII * The Washington Redskins won Super Bowl XVII, then lost Super Bowl XVIII * The Green Bay Packers won Super Bowl XXXI, then lost Super Bowl XXXII Only twice did the loser of a Super Bowl win the following year, and they were consecutive : * Dallas Cowboys lost Super Bowl V to the Colts, won Super Bowl VI over the Dolphins * Miami Dolphins lost Super Bowl VI to the Cowboys, won Super Bowls VII and VIII (see related question for all winners to date)