Great question!
There are several sites that do this, a lot of them vary by state.
Consumer Reports did a ranking of health insurance companies awhile ago, as did US News and World Report (I believe). Try their sites - although you might have to pay for access on the Consumer Reports site. Try these:
http://health.usnews.com/sections/health/health-plans/index.html
http://web.ncqa.org/tabid/60/Default.aspx
It also matters what state you are in... I googled Health Insurance Plans Rankings... which you can do, and then look for sites specific to your state.
Good luck!