There's a popular cycling route around Mercer Island. The road that goes around it, Mercer Way, I think, is twisty and doesn't have too many cars. Which makes it popular with the road biking crowd.
As it's connected to the mainland by the I-90, Mercer Island is a required component of bike rides around the north or south halves of Lake Washington. (I-90 Bridge has a convenient bike lane that the stupid I-520 Bridge doesnt.)
They also have garage sales with good stuff.