Epcot and the MK have incredible fireworks displays, so be sure to head to one of those parks. Get to the parks early, though (read: as close to park opening time as possible), because all four WDW parks fill up quickly on holidays.
We will be spending our first NYE in WDW this year. We are going to try Epcot because it is huge and will absorb the crowd better (I hope) Get there early, is good advice.