I know Disney has done a few sponsorships over the years, which have actually integrated with the parks pretty well. I remember seeing a Kodak piece on the pink Epcot pavement, and how studies showed that the pink helped enhance photo colors in the park. Energizer sponsored Star Tours for the longest time, and had a funny poster series at the exit queue showing the energizer bunny footprints going through the history of time (going and going and going and...).
The WORST sponsorships are train decal sponsors. We saw a slew of these with Six Flags, with hideous pastel colors slapped on coaster trains.
Blegh!