SkinEdit is a simple graphics editor optimized for making Minecraft skins. It got many features to make it easier for beginners to understand how Minecraft skinning works as well as all the features even experienced skinners need. With over 200'000 downloads so far the latest alpha adds many requested features such as dodge and burn tool as well as flood fill.
Here is a video tutorial by a friend of mine if you prefer video over text:
You can download it here or here
If the previewer won't download or won't work, delete skintest2.jar and when it asks for the URL enter this: