I have a hard time accepting any attraction that has opened after 2000 as a "classic," lol. I really only consider opening day attractions and Walt-touched attractions classics... Or old-school dark rides... But they also have to contain some level of quality to be a classic in my mind, particularly at HS and AK.
MK- Tiki Room, County Bears, Tom Sawyer Island, Swiss Family Treehouse, Pirates, Thunder Mountain, Space Mountain, PeopleMover, Peter Pan, Haunted Mansion, Main Street Vehicles, Railroad.... All of the obvious stuff.
EPCOT- Living with the Land, Spaceship Earth, American Adventure, Impressions de France, most of World Showcase... And I will throw a bone over to Soarin'.
HS- Muppets, Indiana Jones, Tower of Terror, Fantasmic, the OG concept of Star Tours.
AK- Dinosuar, Safaris, It's Tough to be a Bug... And I'll throw more bones at Everest and Lion King.