Here's the POD for my first serious timeline:
1860, Stephen Douglas wins the Presidential nomination of the Democratic Party and wins the Southern states, the border states, California (they went Democratic in the past two elections of their statehood, why can't they go Dem in 1860?) his home state of Illinois, and New Jersey (pumping up his railroad platform) and goes on to narrowly beat Lincoln in November.
Obviously, the first major change is secession is immediately averted. South Carolina is temporarily pleased and does not secede from the Union, nor do any other states follow to form the CSA.
What do you think would happen next? Remember that the balance between Free States and Slave States is still uneven. civil war averted, or just delayed? More importantly, what happens in the long run? Border changes, race relations, etc?