I'll second the Mike Bentley site.

You could also check out this site from Chicago Athlete:

http://www.chicagoaa.com/calendar/smu.html

And if you're anywhere near the Chicago area, the Evanston Bike Club has rides of all abilities and distances. Here's their site:

http://evanstonbikeclub.org

And there's also the Chicago Cycling Club:

http://chicagocyclingclub.org