The 4th season doesn't begin until October of this year (as fast as time flies, its already October) but shooting for the next season has begun. As you may remember the season ended with the grand battle between the two camps, the Governor and the Prison, some notable deaths and some crazy good action. What the survivors do in the coming season is anyone's guess (well anyone who read the graphic novels might have a good idea).
But spoilers, just a few are beginning to leak out. New cast member, Lawrence Gilliard as Bob Stookey, some kind of military base, a plane crash. All very cool.