Gran Fondo Guide has extensive lists, although they seem to be rewritten press releases, they are great for seeing what's available.
Active.com has searchable lists for
Centuries and
Mountain Biking. Active handles registration for some events, and might only list events they're running. The cycling stuff is a little sparse, but there are lots of running events.
Non-profit
Columbus Outdoor Pursuits runs many rides in central Ohio, including GOBA and the
Tour of the Scioto River Valley (55th annual ride Mother's Day Weekend!).