Quotes
Popular site that actually allows you to buy policies online:
http://www.ehealthinsurance.com/
Another site that refers you to an agent when you find an optimal plan:
http://www.healthquotefinder.com/
Get quotes from these specific companies:
Aetna:
http://www.healthplanone.com/healthinsurancecarriers/aetna/
Anthem/Blue Cross:
http://www.healthplanone.com/healthinsurancecarriers/anthem/
Celtic:
http://www.healthplanone.com/healthinsurancecarriers/celtic/
Golden Rule:
http://www.healthplanone.com/healthinsurancecarriers/goldenrule/
Humana:
http://www.healthplanone.com/healthinsurancecarriers/humana/
Unicare:
http://www.healthplanone.com/healthinsurancecarriers/unicare/
Further Reading
Consumer Reports is a great unbiased resource that can give highly accessible insight into health insurance-related topics.
foreignborn.com gives a very readable overview of the American health insurance system. It's an interesting outsider's perspective that doesn't leave anything unexplained.