Using Wikipedia
Wikipedia comes up at the top of many searches, and it can be a great resource for certain situations. However, it's important to understand its strengths and limitations.
Be aware that many teachers will not permit students to use Wikipedia as a resource for a project. Others may tell students that they may read it to better understand a topic, but they may not cite it.
I like to tell people that it can be a great place to start to get an overview of a topic or to find links to resources (look at the bottom of the article for "External Links"), but it's not the place to wind up your research. Here is what Wikipedia itself says:
"Students should never use information in Wikipedia (or any other online encyclopedia) for formal purposes (such as school essays) until they have verified and evaluated the information based on external sources. For this reason, Wikipedia, like any encyclopedia, is a great starting place for research but not always a great ending place....
In general, popular Wikipedia articles are more accurate than ones that receive little traffic, because they are read more often and therefore any errors are corrected in a more timely fashion"
There are about 3,100 featured articles (out of over 3 million) - these have been reviewed by Wikipedia's editors for accuracy and completeness. These have a bronze star on the page.
Another 10,000 are tagged as Good Articles. According to Wikipedia, these articles "should be well written, factually accurate and verifiable, broad in coverage, neutral in point of view, stable, and illustrated, where possible, by relevant images with suitable copyright licenses. Good articles need not be as comprehensive as featured articles, but they should not omit any major facets of the topic. "
There are some pages which are protected to prevent them from being changed by anonymous users. Some of these pages are administrative pages, but others are those which have been subject to vandalism, like the Barak Obama page. When you go to this page, you'll see that it is "semi-protected" (see the lock icon at the top), and that it also has a featured star, which means it's been reviewed by Wikipedia editors.
One of the most valuable aspects of many Wikipedia articles are the footnotes and links at the bottom of most articles. These allow one to easily do follow-up research and verification.