HS has the Osborne Lights, usually turning on around 6:00 each night.
Epcot will have a special ending to Illuminations, Candlelight Processional and Storytellers around the World.
MK will offer a hard ticket event, Mickey's Very Merry Christmas Party and the taping of the Christmas parade if you want to see that. (I personally wouldn't suggest it.)
All parks will have some decorations and wonderful huge Christmas trees. MK might not have their tree up when you are there. They wait until after the parade taping.
Resorts will have decorations up, but touring the deluxes would be a fun thing to do. GF has the gingerbread house and huge tree. BW and BC/YC have big chocolate displays. CR will have either a chocolate or gingerbread display. WL and AKL will have huge trees and other decorations. FW offers special carriage rides.
DTD will have a tree and decorations as well.
This is a good start for you. If there is anything that sounds interesting to you, let me know and I'll see if I can give further details.