Angies List is one around here but there doesn't seem to be many good references on it. Your best contractors will be found by working your local contacts to find out who other people in your area have used. Very clearly put your expectations for the subcontractor in writing including, initial deposit, payment schedule, time to completetion, and remediation for problems and any missed deadlines. After you've paid-in-full you have extremely little leverage with a subcontractor to remedy problems so never pay in full until you have thouroughly inspected each and every aspect of the contractors work.
just my .o2, Doug