My complete list would be pretty long, and include classic attractions like Mission to Mars, the Skyway to Fantasyland, Horizons, and the original Animation tour when they were really working on Disney animated movies (anyone remember seeing artwork from Mulan in there?). But the two things that come quickest to mind would be the Lights of Winter in Epcot and the Off Kilter boys.
The Lights used to be a really important part of the Christmas vibe in Epcot. You could see them from all around the World Showcase. And standing under the arches while the show was going on was a totally unique experience. And I've been enjoying Off Kilter for years (at least, the original lineup of Jamie, Randy, Mark, Tony and Scotty Z.). I was there for their final set, and it was truly a special performance. They will continue to be missed.