Well you could goto Flickr and look for CC'd images.
Check the licenses for them, but the idea with most of them is that you can publish them provided you give the photographer credit, with their name near the image somewhere.
For example, these can be used commercially, provided you stick to the rules:
http://www.flickr.com/search/?q=funny&l=comm&s s=2&ct=0&mt=photos&w=all
(Click the 'some rights reserved' link on the right for each image to see what you can and can't use that photo for. That search should only show ones you can use commerically though.)