The venerated BMW R1200GS motorcycle is often thought of as the Godfather of adventure motorcycles due to it's heritage as a Dakar Rally motorcycle and as the choice of RTW travelers such as Ewan McGregor and Charlie Boorman as seen on the documentary Long Way Round.
In 2013 BMW updated the BMW R1200GS. This video is perhaps the best review that I've seen that compares the old air cooled R1200GS and the new water cooled R1200GS. Check it out. (16:34 minutes)