In past years, my two kids have been 11 months and 4, 2 and 5, and 3 and 6 when we went to Epcot. The things they liked best:
The fountains (all of them -- the big one, the one in front, the little squirty ones that got them wet, the upside down one outside the Imagination Pavilion, etc) -- if you are there at night, watch the main fountain on the hour (I think) for a really cool light & sound display. Stopped mine in their tracks every time.
The KidCot stops (again, all of them, every trip, repeatedly)
The movie at the France pavilion
The Living Seas
The Circle of Life movie at the Land (the boat ride was okay too)
Any food stop at all
The interactive displays at the Wonders of Life and Imagination pavilions -- I spent a lot of time there with the little one while my husband and the older one went on the bigger rides. There's a suprising amount to keep a 2 year old occupied, especially at the Life pavilion!
Test Track (the older one rode it each time -- she's tall and made the height cut off even on our first trip -- and the younger one liked playing with the stuff in the waiting area)
Ice Station Cool.
They did NOT like:
Universe of Energy (too long and over their heads the first trip)
Cranium Command (it is a great show, but they just didn't like it)
Maelstrom (terrified the heck out of them both)
The Canada movie (no seats, they had a hard time seeing, the little one wanted to be held, which is a killer on the back)
Food Rocks (way, way, way too loud)
Hope that helps!