MUST rides are:
Splash Mountain**
Big Thunder Mountain**
Pirates of the Caribbean
Haunted Mansion
Space Mountain**
Those are the biggies
Fun, and try not to miss:
Peter Pan (quinessential Disney)**
Mickey's Philharmagic**
Buzz Lightyear**
Tomorrowland Transit Authority if you are waiting for your FastPass window for Buzz or Space Mtn. A great way to see Tomorrowland!
I think the Jungle Cruise captures another type of Disney spirit; as does Carousel of Progress, but if you are pressed for time, skip them.
**- these rides have Disney's Fastpass- a way of 'reserving' your place in line for the popular rides, while you go do something else- grab a bit to eat, go on another ride, etc. You will insert your park ticket into the fastpass machine, and it will give you a 'chit' of a window of a one hour time to come back for your turn, with only a minimal wait time. It's great! For instance, when we go, we go to Frontierland first, grab a FP for Splash and beeline to Big Thunder Mountain and ride that. Then you can do another ride perhaps, and go back and ride Splash without a wait. Hope this helps!