We were absolutely dazzled by the Osborne Lights at DHS...it is fantastic, and see it every chance you can!
We also were charmed by the stories of the Santas around Epcot's World Showcase -- definately worth taking the time to see, especially while snacking around the world.
The Candlelight Processional at Epcot is also very beautiful, but not appreciated much by young kids, so just loiter at American Showcase to listen if you have young kids in your party, otherwise it is worth the time in line or making dining plan arrangements to see this.
All of the above are included in regular admission.
Also be prepared to find yourself buying a fantastic seasonal hat and wearing it during your trip, only to get home and say "what was i thinking!!"