Just had to post this pic of a bus wrap from the streets of Copenhagen for the Copenhagen Zoo. This wrap was designed by Bates Y&R in Denmark. (Thanks to adsoftheworld.) That's some printing and installation job!
If you want to see more, a couple of blogs have published great galleries of bus ads lately. Check out Oddee for example. This can give you some ideas to get the creative juices flowing.
Of course, everything is easier on the super large canvas that a bus offers.