I am familiar with the attractions that have stairs, here is a detailed list:
Main Street train station had no way to avoid stairs
Main Street transportation has steps up into the vehicles.
Great moments with Mr. Lincoln has steps, enter through the doors that wheelchairs and
ECVs ate directed to in order to avoid steps and steep slopes.
Tiki room has stairs that can be avoided by asking for the lift.
Jungle cruise has stairs on busy days
Indiana Jones has stairs in both the queue and the exit.
Tarzan's tree house has an accessible path to the activity area near Pirates.
Pirates does not have stairs, but has steep ramps in the normal queue
New Orleans square train station has stairs, there is a ramp near Haunted Mansion
Splash Mountain has stairs in the traditional and FP queues.
Tom Sawyers Island had since stairs and steps, accessible paths are available.
Sailing ship Columbia had stairs that cannot be avoided for boarding.
Big Thunder had stairs in the queue prior to the rehab, Rumor has it that these stairs may be removed from the queue during the rehab or may get an elevator.
Casey Jr has some steps up to it, they can be avoided by using the accessible route or asking the CM working there.
Sleeping Beauty Castle walk through has stairs, an alternate viewing experience is available.
There is a step up for the Carousel, a ramp is available.
Peter Pan has a couple of minor steps in the regular queue, or at least it used to.
Small word has stairs at the exit
Fantasyland theater has stairs that can be avoided by asking for the accessible path.
Autopia has stairs that can be avoided by asking for the lift.
Monorail has a very steep ramp that they call am accessible ramp; however, it does not meet the requirements sure to slope and length. There is an elevator available that they don't like to let you use, but will if you are unable to use the ramp.
Finding Nemo inside the subs, an alternative experience is available.
Innoventions had a steep ramp that they don't even pretend is accessible. There is an accessible route available. There are also stairs inside, an elevator is available.
Space Mountain has stairs at the exit.
Star Tours has a steep ramp in the normal queues.
At DCA:
Aladdin has stairs, you must have an
ECV, wheel chair or DAS to avoid.
Tower of Terror has stairs after the loading room on the left.
Radiator Springs racers has stairs at the exit
California Screamin has stairs in the queue and at the exit.
Silly Symphony Swings has stairs, an elevator is available
Golden zephyr has stairs, an elevator is available.
Goofy's Sky School has stairs at the exit
World of color has steps, accessible paths are available
Grizzly River run has stairs at the exit. Alternatives are available, just ask.
There are steps in Redwood Creek challenge trail, there are accessible paths.
Soarin' has a step exit ramp, alternatives may be available, depending on the CM.
Red car trolley has a step up, there is an alternate loading method available that can avoid this, it is intended for wheelchairs, but has handrails and can be used for those that can't handle the steps.