I generally agree with the rankings in this thread, except for the olympics. The olympics have a short history 4 olympiads. I think their prestige will go up and down depending on the course. If the measure is prestige of the fields and who makes the sharp end of the race, take a look at the olympic top 10 over their history. In beijing, a number of top cyclists made the olympics a targetted race. In other years with a softer course less riders will focus on it, but they may still ride for patriotisms sake. The 4 year thing can work for or against them. Being rare makes a gold medal valuable, but even 1 poor olympics is 8 years between top riders contesting the medals.
Olympics winners. Pascal Richard, Jan Ullrich, Paolo Bettini, Samuel Sanchez
Podiums. Rolf Sorenson, Max Sciandri, Vinokourov, Kloden, merckx, Paulinho, Cancellara, and Kolobnev.
For me the jury is out on where the olympics will find its place. London really screw this.