K.J.
I've had great success with Sitter City, but I mainly chose that avenue as I do not know many families who use sitters, so I didn't have the option to ask others for recommendations.
I have had my Sitter City membership for about 2 years, and I have found it well worth it. I have interviewed about 10 sitters, and would use all but maybe 1 of them. It's very nice to have a slew of babysitters on hand so that if need be, I can call any of them for emergencies.