I use an electric wheelchair full-time and can't sit up without complete support.
When the map says
ECVs must transfer-it is talking about the 3 wheeled scooters or the chairs Disney rents NOT electric wheelchairs. Here is a list of rides that you can drive your wheelchair directly onto without transferring, sorted by park:
Magic Kingdom---
Buzz Lightyear's Space Ranger Spin:
Stitches Great Escape
Many Adventures of Winnie the Pooh (Takes you through several classic scenes-awesome-easy access)
its a small world (easy access)
Liberty Belle Riverboat (Tour around a lake with some props and animatronics-kinda long-chair sits below level of bars, partially blocking view)
Main Street U.S.A.-Railroad-steam train ride (I loved it. Round trip is best, there are scenes along the way.)
Jungle Cruise (recently converted)
The Magic Carpets of Aladdin
All the Character Greeting Areas and shows are wheelchair accessible. There are always spaces for wheelchairs with seats for family members adjoining
Swiss Family Treehouse and Tom Sawyer Island are impossible for wheelchairs (you can do a roundtrip on the raft that goes to Tom Sawyer Island)
All night-time shows and parades have special wheelchair viewing areas-ask a CM, they're marked on a map- arrive 1-2 hours early for a seat and you cannot leavenighttime shows are my favorite and are well worth the wait
Spectromagic parade (nighttime parade of lights)
Wishes Fireworks does NOT have specified wheelchair seating
Epcot
Ellens Energy Adventure (easily accessible-cute Jeapordy style beginning that then takes you back in time to Dinosaurs)
Journey Into Your Imagination (easily accessible-really cute/fun ride with a fully accessible interactive special effects playground afterwards)
Living with the Land (informational tour about various climates and agriculture)
El Rio Del Tiempo (accessible-boat ride tour of Mexico)
The Living Seas (all areas accessible, although some areas may have alternate access. At your own pace viewing of a live sea aquarium and the new Crush attraction)
The World Showcase (all areas accessible, although some areas may have alternate access)
Street shows are hard to see unless you arrive a little early to sit in front
All the Character Greeting Areas and shows (including Innoventions) are wheelchair accessible (*note: The Kid cot fun stop crafts will be difficult to do unless you have a tray on your wheelchair because the table and chairs are low and the supplies are scattered)
All night-time shows and parades have special wheelchair viewing areas-ask a CM- arrive 1-2 hours early for a seat and you cannot leave-- nighttime shows are my favorite and are well worth the wait
MGM Studios
Great Movie Ride
All the Character Greeting Areas and shows are wheelchair accessible
MGM has a lot of good shows
All night-time shows and parades have special wheelchair viewing areas-ask a CM- arrive 1-2 hours early for a seat and you cannot leavenighttime shows are my favorite and are well worth the wait
Animal Kingdom-
Wildlife Express Train (train that shows you how Disney cares for their animals and takes you to the Conservation Station-may have to back on)
Triceratop Spin
Kilimanjaro Safaris (mild thrill ride with a guide that drives you through authentic habitats to view real exotic animals-best experienced in the morning. Note: This ride is bumpy. You may need to back in to the ride vehicle.)
All the Character Greeting Areas and shows are wheelchair accessible (*the Boneyard is not. *Conservation is listed as accessible but I didnt visit it.)
All the nature trails are accessible and have beautiful wildlife. There are many exhibits-a few viewing areas are a little difficult to get to.
All night-time shows and parades have special wheelchair viewing areas-ask a CM- arrive 1-2 hours early for a seat and you cannot leavenighttime shows are my favorite and are well worth the wait
Flights of Wonder (bird stunt/aerial flying).
I hope I helped.
Remember all shows are wheelchair accessible-don't miss the nighttime shows-especially Fantasmic-and don't miss Festival of the Lion King.
If there is anyway to transfer, I would do it for Soarin in Epcot. The ride is awesome. Even I was able to do it. You can pull your chair right up to seat and the movements of the ride are smooth. The seat is also elevated.
And here is some more detailed information from my recent trip:
I just returned from Disney World. There were some rides that I couldn't go on that I thought I could. I also have some viewing/ride access tips.
Epcot
Ellen's Energy Adventure: They refused to let my electric wheelchair on. I went back four times on three different days. It was always the same guy. We tried explaining it was not an
ECV but an electric wheelchair. We showed him the disability guide. Nope. He said only manual chairs and something about an accident. Definitely a low of the vacation because it is the only ride we can all ride together and one of Dad's favorites. I would like to report the guy...
Turtle Talk with Crush:
There is a separate wheelchair line. It is to the left of the long line. You might be given a return time. A girl in a wheelchair was allowed to sit up front with the kids (towards the back) but the parent had to ask.
Soarin':
Cast Members request that you park by the pole and walk (or are carried) the few feet to your seat. They will allow you to park right next to the seat and move your chair if you request it. Since I have breathing problems, I pulled the seatbelt all the way out looped it around the armrest (a tip I got from the Pooh sized thread). I was completely secure. The second time I rode a cast member made me unloop the seatbelt but I left it slack and was fine. I also used the strap between the legs for extra security. Grandma held my right arm and Dad was on my left with an arm in front and an arm in back. I was very secure-no problems-and I cannot sit up in any chair or surface (besides my wheelchair) without being held up. DO NOT ask if you can have a family member support you on the ride (made this mistake at DL).
Living with the Land:
Two wheelchair boats with one spot each. No FP needed-separate wheelchair entrance. You may be given a return time. We had a slight problem being allowed on this ride. At first the cast member said they only allowed Hoveraround chairs (???) but after my mom explained that experienced drivers of electric wheelchairs can make very tight turns, he let us on. You may have problems depending on the CM. Those who have problems using steps can walk down the ramp in the wheelchair boat.
Journey Into Your Imagination with Figment:
2 wheelchair cars with one spot each. The easiest wheelchair slot. Drive forward, the CM twists a platform and you face forward. At the end, the CM twists the platform and you drive off facing forward down a ramp. My chair was a tight fit. I took off my footplates. At the end, there is an effect that may cause a startle reflex.
Honey I Shrunk the Audience:
Separate wheelchair entrance-no FP needed. You will probably be given a return time. Unless you transfer to a seat, you will not get all the effects.
El Rio Del Tiempo (Mexico):
2 wheelchair boats-one spot per boat. The seats are pretty low if you transfer. There is a separate wheelchair entrance. But if you have trouble walking do NOT park your chair outside because you will not be allowed in the wheelchair entrance. We got separated from my Grandma this way. She was fine but walking the cue would have been bad for mom because the line is on a sloped surface. There is space to park about 4 chairs by the ride and you can transfer from that point.
The American Adventure:
You will be directed to seating in the very back unless you request the handful of seats up front (we sat in the back)
Illuminations:
Several of the wheelchair seating areas have trees blocking the view. The seating area by the Refreshment Port and by bathrooms (including Companion) does not and has a great view.
Epcot has good Companion Restrooms. You can get a list of the locations at allearsnet.com and First Aid at the park
Magic Kingdom
Tomorrowland
Buzz Lightyears Space Ranger Spin:
I did not fit even though I fit SueM's wheelchair measurements. My midline control was in the way. My sister almost fit but not quite. She might have fit without her desk.
Stitchs Great Escape:
Only manual chairs are allowed on this ride. The batteries and different style backs prevent the electric wheelchair from getting into the proper position. She also specifically mentioned my headrest. So if you have a bulky headrest or one with a long support backing you may have a problem.
Carousel of Progress
Wheelchairs are parked on a slope.
Fantasyland
its a small world:
2 wheelchair boats with spots each. Enter through the exit.
Mickeys Philharmagic:
!! The wheelchair spots experience all the special effects!
Many Adventures of Winnie the Pooh
1 wheelchair car with one spot. I thought backing in was easier. Request the bounce button be switched on for more affects.
Adventureland
Magic Carpets of Aladdin
Only accommodates manual wheelchairs. The device that secures the wheelchair goes between the front and back wheels and is about 6 inches tall. Batteries get in the way.
Accessible stations for the railroad are Main Street, Mickey's Toontown, and Frontierland. Two wheelchair spots.
Spectromagic & Wishes viewing tip:
If you plan to watch both use the Spectromagic wheelchair viewing area by the partner statue. Then you are situated for a great view of Wishes-just turn around. They do make two rows of wheelchairs for the parade...
Disney's MGM Studios
Star Tours:
There is a nonmotion ride available! I was thrilled to know this. There is a separate wheelchair entrance so no FP is needed.
Indiana Jones Epic Stunt Spectacular:
Ask to sit up front for a better view...stay after to meet Indiana Jones.
Backlot Tour:
2 wheelchair spots...I don't know how many accessible trams there are. Mom walked up the ramp to transfer.
Journey Into Narnia:
3 or 4 wheelchair spots-depending on the CM. We fit four (barely).
The Great Movie Ride
2 wheelchair trams with one spot each. I took off my footplates and extra bags and fit (barely) by backing in.
Beauty and the Beast:
Ask to sit up front for an excellent view. Those in ECVs may be asked to transfer.
Tower of Terror:
If you can't ride, you can still watch the pre-show.
Fantasmic!
CMs will direct you to where to sit (you can't pick). Wheelchair spots are marked and have a comfortable amount of space between them.
I had a hard time locating the Companion bathrooms. One of the best bathrooms (female) is the one located just outside the entrance to the park. The stall is as big as a companion restroom and has a sink. It's usually empty or has very few people.
Animal Kingdom
Kilimanjaro Safaris:
2 wheelchair vehicles with one spot each. I find it easier to back in.
Festival of the Lion King:
This show has some of the best wheelchair seats. I also happened to be at the sign language shows. I found my self watching the interpreters because they were so good. There expressions and body language showed the emotion of the music...
Remember that all shows in all the theme parks have wheelchair seating.
If park time will be limited due to pain/stamina issues-you may want to consider a GAC.
Christamae
www.caringbridge.com/ca/oellacz
He also can not walk short distances. It hurts him too much. so i was just wondering what rides he would be able to ride?? Also i am willing to transfer him if needed. He is a big guy around 260-280. 
