The "Cityrama" from the 1960 movie; "Zazie dans le métro" .. the Citreon U55 Currus

Skip right to the 3 minute 49 second mark to see it in action: http://www.youtube.com/watch?v=00d_XAvG190

http://en.wikipedia.org/wiki/Zazie_in_the_Metro and http://www.imcdb.org/vehicles_make-Citroën_model-U55.html

and update August 2012, http://www.darkroastedblend.com/2012/06/most-extravagant-bus-ever-built.html has a great gallery