I was reminded of this trick while browsing Lifehacker. You can limit your search results in Google to show only educational (.edu) sites.
To do this, type the following into Google:
site:.edu "search topic"
Lets say I wanted some photos that were royalty free or free for educational use. It might be helpful to limit my search to edu sites so I type in:
I did this and discovered this cool gallery of crocodile photos sponsored by the University of Florida that are free for educational or non-profit use.
That's where this neat picture was hiding.
[Image: King, F. Wayne. "American crocodile, Crocodylus acutus.." Crocodilian Photo Gallery. 1996?. Florida Museum of Natural History. 9 Oct 2007