In a nutshell-
The Hobbit:
Thorin Oakenshield and Gandalf visit Bilbo in the Shire. Bilbo joins the Dwarves' quest. Bilbo meets Gollum and finds the One Ring.
Bard slays Smaug the dragon with the aid of Bilbo. The Battle of the Five Armies—Men, Elves, Dwarves, Goblins, and Eagles— is fought over Smaug's treasure. Thorin Oakenshield dies in battle, and Dain becomes King under the mountain.
The White Council meets again and Saruman, hoping to keep Sauron from finding the One Ring, agrees to attack Dol Guldur. Sauron abandons Dol Guldur.
Bilbo returns to the Shire and begins to write his memoirs, the first volume of the Red Book.
Post-Hobbit
Sauron returns to Mordor.
I'm guessing this is approximately where the second movie will end. There really isn't much that happens between this point and the beginning of Fellowship, 60 years later. Mostly just Sauron rebuilding his forces and Aragorn ranger-ing about. Gandalf wanders around some and Saruman finds the Palantir.
I'm not really sure how this will play out in the movies. They compressed a lot of time in the 3 LOTR movies. For instance, it was 20 years between Bilbo's birthday party and Gandalf returning to tell Frodo about the true nature of the Ring. The rest of the movies play out over the course of a year, but the movies make it seem like a couple of weeks.
My guess is perhaps they would end the first movie as Dain becomes King, and perhaps have Bilbo returning home and Sauron being driven from Dol Guldur in the second.