http://www.smashingmagazine.com/2010/03/30/the-ultimate-guide-to-cloning-in-photoshop/ The article, "The Ultimate Guide to Cloning in Photoshop" comes from Smashing Magazine. The magazine, targeted to designers, lists the many cloning tools that can be used in Photoshop to alter an image in any form. It also gives a brief tutorial on how to use each tool.
The tool that stuck out the most was the brush tool when cloning. For one, I didn't understand the difference in the result of the hard and soft brushes. The article states that a soft brush gives a much smoother transition and therefore makes the best result. A hard brush has a more noticeable transition.