When I prepare a PowerPoint presentation, one of the most difficult things for me is typically finding good pictures that I can use as visuals in my presentation. Just to make things difficult, when doing this, I prefer to use photos that I have the right to use. Matt Homann (who always has great advice) links to a post that provides 37 paces to get free stock photos. Matt also provides a link to his two favorite places to get photos: Every Stock Photo and Stock.xchng.
So, the next time you are in need of a photo, you now have some resources you can use to find the perfect picture to represent your point.