Jason has a great write up about the advantages of using a flash diffuser and an off-camera flash. He has a bunch of great examples, and a nice tutorial at the end of his article. After seeing the results, you will want to try it out too!
I’m going to talk about how to make a cheap slave flash, and, how to make a free / super cheap, on camera flash diffuser for Nikon, and really any other camera with a pop up top flash
More about DIY: Cheap on-camera flash diffuser