I am sure there are other centuries as well, but Ryan Wood missus a big one - the Horrible Hundred in Clermont, Florida. See: http://www.horrible-hundred.com/hhindex.php
This ride is in its 32nd year, and the last couple years has sported around 2,000 riders. Beautiful countryside, and some steep, rolling hills that include Sugarloaf "Mountain."
jon anthony blumhagen
And this one!