We've brought together a few websites that do a good job of explaining the criteria to use when evaluating websites you find during your research.
UW-Washington County Checklist for Evaluating Web Sites - This checklist is a good tool when evaluating web pages.
Five Criteria for Evaluating Web Pages - Cornell University Libraries has put together this concise guide showing the five criteria and explaining how to interpret them.
Evaluation Criteria from Susan Beck's The Good, The Bad & The Ugly: or, Why It’s a Good Idea to Evaluate Web Sources.
Evaluating Web Pages - UC Berkley Library guide for evaluationg web pages gives you questions to ask yourself and the implications.
Internet Detective tutorial on web sources.