I could only think of a handful of these, but some just have always stuck with me. Which is most memorable to you? (There is an option for 'other', in case I've left one out or you have another in mind.)
Splash Mtn - The mildewy, wet smell of the ride logs.
Space Mtn - The odor of the ventilation system within the building.
Spaceship Earth - Rome burning.
Soarin - The smell of pine or oranges.