Beauty and the Beast is one of my favorites.
Festival of the Lion King at Animal Kingdom (Camp Minnie-Mickey) is fabulous. Finding Nemo the Musical, also at AK isn’t one of my favorites (actually, I rather dislike it), but it’s very popular. Flights of Wonder at AK has a rather corny plot, but the birds are fun to watch.
The Dreams Come True show at Cinderella’s Castle is fun and should be watched at least once. Also, around the holidays, there are shows in the Tomorrowland Galaxy Theater (The Night Before Christmas around December/January).
Epcot doesn’t have any big musical productions, but there are lots of shows. The Jammitors are very entertaining. Travel around World Showcase and catch the Chinese Acrobats. America Garden Theater hosts many different shows throughout the year (here, I’ve seen Blast!, Shockwave, and The ABBA Generation).
High School Musical at Hollywood Studios is fun for the kiddies, but probably not very entertaining if you haven’t seen or cared for the movies. The new Block Party Bash is lots of fun and very interactive. Then there’s always Fantasmic, which I personally do not care for, but it draws a big crowd.