There is a new website called HiveMoms where you can find nearby moms to trade free babysitting on a points system.
It's a great way to build a group of mom friends who take turns to care for each other's children, so that everyone gets a chance to take a much-needed break. The website makes it easy to keep track of the points, and best of all, it's free!
The url is http://HiveMoms.com/. Maybe there's already a babysitting co-op that's right for you!