One of the Harleys ridden by Peter Fonda in Easy Rider is expected to fetch over a million dollars at auction
http://www.bbc.co.uk/news/entertainment-arts-29235391
I reckon this would have to be the most iconic motorbike ever.
Some folk might come up with their own favourites, particularly race bikes like Slippery Sam or the 500 MV Agusta but none as recognisable as this.