Wikipedia describes itself as "the free encyclopedia anyone can edit." Read Wikipedia's ever-growing list of disclaimers--"Wikipedia Makes No Guarantee of Validity." It's not a good idea to rely on the information you find here--you can use it to start your research, but never quote from it in a research paper.
Factors to look for in evaluating websites include
- Site requires registration
- Site is fee-based or licensed
- Site is behind a firewall or on an intranet
- Site is dynamically generated