I've been riding my bike a lot, because my son is back in town for the summer. We're looking into "The Orient Express" trip -- as detailed here:
http://www.tourdafrique.com/orientexpress/index.html
The same company runs a trip across Asia, Africa, and South America (lick on the upper right to check them out) -- but they're longer and I'll have enough trouble getting off work for the two months it takes to bike from Paris to Istanbul.
Looking at the route, there's a bike path from the French border all the way to Budapest -- so if I can't get off work, maybe that would be a good ride.
We haven't looked into competing professional tours (or the idea of a do-it-yourselfer along the same route). I guess that will have to wait until we get back from our whitewater rafting trip in Utah.