Flickr or Stock Exchange. There are great photos there, but it's tough to find them. The search tools and tagging system on most photos sites just don't provide a robust experience. Google is great at searching and Google Images is great for searching for images. The problem is that many of the image results that will come up from Google will be either copyrighted or too small or both.
If I'm looking for images for a specific thought or point I'll use Google Images to find the photos that are close to what I want then move on to the higher quality resources to put in my presentations. Google Images allows you to search by keyword, file type (photographs, line drawings, and faces), color, and size.
How do you search for the perfect image?