Ratatouille! Incredibles (a ride, not the artist sit-through)!
And Cars!!!!
They should re-do Test Track into a Cars ride. It wouldn't take much at all, and the end would dump your "car" out into the Piston Cup (he did what in his cup?) -- in other words, don't change a thing with the actual run on the Test Track; just some minor changes to the inside. Doc Hudson could narrate in the inside taking you from all the "stops" that we love from the movie, i.e., the Cone Motel with Sally, the Tire Shop with the Italians, the militant and hippy cars and, of course, the junkyard with Mater. Or Mater could narrate and one of the "stops" could be the garage or courtroom where you get to see Doc. Or Mack could narrate the whole thing and imagineering includes both a Mater and a Doc Hudson scene.
The part of Test Track where you're currently in that boring black room waiting for the doors to open to let you out onto the track could be done up just like the inside of Mack's trailer when Lightning is in it -- with maybe one of the popular songs from the movie in the background.
Naturally a photo is taken with a Cars theme around the border -- heck, maybe they could even superimpose Mater or Luigi "sitting" in the back of your car.
As much as I would love a Ratatouille ride, I wouldn't be surprised if they bring him in somewhere with dining, i.e., a character meal of some sort. It would be great if it could be some sort of gourmet kitchen that allows for observation and/or a little interaction by its patrons. Maybe a character meal that appeals to adults (I say this only because I know more adults who enjoyed this movie than children)