I would enjoy a full-fledged feature length film involving crossovers between any number of Disney characters akin to the Kingdom Hearts games... Or even the House of Mouse cartoon series.
Something like an adventure in which Disney Channel Stars must team up to save something/someone. They've already established that these characters live in the same world so why not try capitalizing on the popularity by making a lavish production film.
I wouldn't mind seeing some other crossovers either.
Off the top of my head...
Transformers & G I Joe
Marvel vs. Capcom sounds like it might make a pretty damn cool anime
Marvel vs. DC
Family Guy vs. The Simpsons (Maybe... I don't know if it would be any good honestly.)
Super Mario Bros. vs. Sonic the Hedgehog
Star Trek vs. Star Wars
And my all time favorite crossover idea... Bringing true closure to three of the greatest series of the 1980's... Transformers vs. G.I.Joe with Special Guests Jem and the Holograms... Or as I have coined...
G.I.Jem: More Than Meets the Eye.
Actually now that I think about it I wouldn't mind seeing a Crisis of Infinite Earths type of things involving the current DC Animation Projects, The Batman, and also... The DCAU of the 90's and early 2000's. Can you imagine, The Justice League fighting against the characters from Batman Brave and the Bold with The Batman thrown in just for some insanity and maybe even as a throwback nod the old 60's and 70's Superfriends too? It would have to be 2 hours and totally EPIC as all get out.
Apache Chief might have to be left on the side-lines though due to politically correctness stuff.