Use the following 5 W's to evaluate web sites:
Who is responsible for the creation of the site? Do they have listed credentials? Are they associated with a reputable institution? Can you contact them?
What is the purpose of this site? What is the URL of the site and what might that tell you about its purpose? What aspects of the site make it difficult/easy to use? (For example: typos, easy navigation, nice layout, images, too much advertising, etc.)
Where is this information coming from? Is there a bibliography or listed references? Is the site listed with an established institution?
When was the site last updated? Does the site even have a date? Does the currency of the information directly impact your subject?
Why is this website useful for your research? Is it necessary for your research or could you find the information through a better source?