Contractor reviews are available on a number of websites, such as Home Advisor, Angie's List, 1-800-Contractor, Homestars, and Rate My Contractors. All of these are sortable by ZIP code and the type of job.
All of the above review sites are free with the exception of Angie's List, which operates on a subscription model. To justify the cost, the company claims the benefits of no anonymous reviews, certified data collection and a Complaint Resolution Team that acts if something does go wrong. Since all of the above websites feature user generated reviews, the possibility exists that one discontented customer will overshadow multiple satisfied customers that chose not to write a review.