Well, I'm settling into my senior year and a rigorous social life as near completely replaced my rigorous academic life. Anyway, I will have some time to get back to this game, so here are some ideas.
Andrew Johnson's Reconstruction program succeeds and the Southern states are back into the union and voting in the election. Johnson is still charged as an incompetent by critics but his modest success in bringing peace has gotten him renominated. He faces US Grant who actually campaigned with him to pass Reconstruction bills.
(you could really go farther with this concept, considering other elections running against johnson's legacy and the eventual split between north and south again)
Tilden Re-election campaign. I'm sure you're all aware of the 1876 contest, What if it went the other way?
What if Cleveland won in 1888 (he really did get the pop vote)?
WJ Bryan re-election
TR doesnt run
Hughes Re-election (1916 was exceptionally close)
Truman assassinated in 1950 (there was an attempt)
Nixon realizes there's no reason to spy on mcgovern, who he clobbers. successor race
Carter won in 1980, cringe
Clinton runs again and must run for reelection in 2000?