The Door County Century is a really nice ride, but if you are looking for something earlier in the season I'd suggest the "Trek 100".

http://www.maccfund.org/trek08/

I have done it the past three years and it is one of the best organized events in the area. The routes are really nice and the rest stops have unbelievable food. I can't say that I've ever gotten "Famous Dave's" wings and bread pudding at any other cycling event.

The best part is that it's for a really good cause.

Trek always brings in a celebrity to lead off the ride. Last year they had Lance Armstrong.