Well, I just moved to OR so I haven't any favs out here yet although the Cinderella in CA was very cool.
Back home in Lancaster, PA (Amish country) my former bike club has the covered bridges ride... http://www.lancasterbikeclub.org/cbm.php which is a century ride. They deliberately made the route not too hilly to encourage people to ride because that area is not known for liking biking. The other one I could suggest is the Bucks County Covered Bridges ride. http://www.cbbikeclub.org/?body=cove...04872fbdbec185 That one is very hilly and tough. Even the shorter routes are nasty. The scenery is gorgeous though. They were a little disorganized last year. The way it was setup, you could have actually ridden in it without registering and no one would have known. They had complaints about it so hopefully they will get it together at the start this year. The shirts are great though. They have a local artist do a painting of one of the bridges each year and feature it on the t-shirts. Like I said, you truly earn that shirt with every revolution of your pedals though.