good question!
my must do's are:
1, Disney parades, shows, evening entertainment, sounds like a lot but the free shows and evening fireworks are worth the entrance price alone!, mgms fantasmic is THE best show! illuminations at epcot, wishes and spectromagic at Magic Kingdom, oooh! I could go on, as you enter each park there are times guides to pick up, little show like the pirate show in Magic Kingdom with the johnny depp cap'n jack sparrow-alike

love: ) are definately worth seeing.
2, At least one of the disney water parks, they're both great and I personally love Typhoon lagoon best but a day in either one is not to be missed.
3, Character meal - sorry but just sums up the whole experience, really makes you feel like a child again and is great fun and a good photo op! do your reasearch though as some have on going notoriously bad reviews!
4, Seaworld, a totally different park idea to Disney, and great fun, allow a full day and you'll get pretty much most of it done, it is tiring though and as with all parks it definately pays to study the map upfront and work out YOUR must do's
5, shopping - try premium outlets, mall at millenia and florida mall for the best mix of all types of shops - I'd seriously try and allow 2 or 3 days out of 14