Limiting your search to specific domains (.edu or .gov) can remove some of the less reputable websites from your Google searches.
.com - commercial or business
.edu - educational institution
.org - organization (often non-profit)
.gov- government organization
Evaluating Web Pages
Whenever you are considering using a website as a source, it is very important that you review the contents in detail. An easy way to make a determination is to use Jim Kapoun's Five Criteria for Evaluating Web Pages:
Accuracy - Can you find an actual author? Is the contact information provided correct?
Authority - Does the author have any credentials? Have they conducted any research? What makes them an expert?
Objectivity - Is the information biased? Are they linked to other organizations (especially commercial)?
Currency - When was the last update to this website?
Coverage - How in depth is the material? Is it basic, informative information you can get anywhere else?
There are many other resources to evaluate web pages easily accessible through the Web. One of the more interesting examples is CSU Chico's CRAAP Test.