I feel very fortunate to be a part of, and ride with, one of the best clubs I've heard about - the Plano Bicycle Association. We have 8 rides on Saturday (and several more during the week) which start with the 16 mile 11-12 MPH average no drop novice ride and move up all the way to the 45-65 mile (depending on which route) 18-21 MPH average ride.
I agree with Crazy88s - riding with faster folks is one of the best ways to get faster and stronger yourself. Then again, I like finishing a ride with my legs and chest burning from the exertion...if that's not your cup of tea that's OK too.