Wikipedia:Tip of the day/August 11
To limit Google searches to the English Wikipedia, include this in your search string: site:en.wikipedia.org.
You can even do a google search of Wikipedia from Wikipedia's own search box! For example, to use google to search for pages with "geology" in the title, type this into WP's search box: google:geology+site:en.wikipedia.org
This link does the same thing: google:geology+site:en.wikipedia.org.
Another way is to use Google's advanced settings. (To get there from Google's search page, click on the gear icon).