Check out the Seattle Bicycle Club Maps Library at http://www.seattlebiketours.org/members/library.html. They have a whole bunch of rides from short to long. I like the south county rides myself, but that's where I live. For the ones less than 100, you can usually pretty easily add some at the beginning or end. For example, when I did the loop around the lake, I added some at both the front and back to come to a full century.