We agree with all of the above, and would add:
MK:
Pirates of the Caribbean (it's a classic for a reason!)
EPCOT:
Body Wars
Cranium Command (it's hysterical)
Don't miss ILLUMINATIONS! (start looking for a spot no later than 20 mins. prior to the start)
MGM:
Star Tours
Don't miss FANTASMIC!
AK:
Dinosaur
If you can squeeze them in, be sure to explore some of the resort hotels, they are truly unique. It doesn't need to take a whole lot of time. From MK, you can take the monorail to 3 of the best- Grand Floridian, Contemporary and Polynesian. From Epcot, you can go through the International Gateway and it's a short walk to the wonderful Epcot resort area- including the Boardwalk, Yacht and Beach Club, Swan and Dolphin.
And, if you're still up for more, visit Downtown Disney, including Pleasure Island (be sure to go the Adventurers Club; one of our favorite spots in WDW!)
Have a great time! You won't BELIEVE how much WDW has changed since you were there!!