My favourite way to find photos (especially for publication in blog posts and use in presentations) saw a big upgrade today: Flickr's search results page is now a whole lot easier to browse.
(Click the image above for a closer look.)
When you search for photos by keyword on Flickr, you get a grid of thumbnails, each of which pops up full-sized versions in-page. (No more having to click to a new page to see what the image looks like close up and other stats.) You can set how big the thumbnails should be, and also sort results by Flickr's magical (and very useful) "Interestingness" rank.
To find Creative Commons-licensed photos only you still have to click on the "Advanced Search" link; but you can bypass that step with a little URL hacking. Append &l=cc to your search keyword shortcut to limit Flickr results to re-publishable images. Firefox keyword bookmark users: the full Flickr CC image search bookmark URL should be http://www.flickr.com/search/?q=%s&l=cc. (Use &l=commderiv for images licensed for commercial use and derivative works.)
When I need to find quality photos that are licensed for reuse in my own work, I hit up EveryStockPhoto (which includes Flickr photos) and Flickr itself—and almost always find what I need without even touching Google Images.