There are many different search engines. Each can give you different results for the same search. Learn to use 2 or 3 search engines by reading their search tips. 

Popular Search Engines include: 
Ask Jeeves - www.ask.com
Exalead - www.exalead.com 
Google - www.google.com 
Scirus - www.scirus.com (For scientific information only)
Teoma - www.teoma.com
Vivisimo - www.vivisimo.com
Yahoo! search - search.yahoo.com

Basic Strategies for Search Engines: 
1. Be familiar with the search tips for each search engine 
2. Check for proper spelling and typos! 
3. Be specific and use phrases, rather than single words 
4. Should phrases be typed in quotation marks, i.e. "global warming" or "acid rain" 
5. Can you use AND, OR, or NOT?
6. Can you use + or - before words 
7. Does it allow for truncation or stemming? 

For more information on searching, try:
Searching the Internet: Frequently Asked Questions

For a more detailed explanation of the different Search Engines and Directories visit the: 
InfoPeople Search Tools Chart