If you're evaluating a web site with medical or health information then HONCode, Health on the Net Foundation's Code of Conduct, is also worth a visit.
 

Citation:
Another common dilemma is determining the proper format for citing sources that you do use.  Here are a couple of sites that address the issue:

Guide to the American Psychological Association internet citation format (prepared by University of Michigan Library)

Guide to the American Medical Association's internet citation guidelines (prepared by the University of Washington's Health Sciences Library)