Dr. Bronners. It's the stuff. http://www.drbronner.com/soaps.html

It can be found at any decent outdoor shop. Hemp based and completely biodegradable. You can even wash your hair and brush your teeth with it. I don't really recommend the latter (bitter taste), but I used to do it when I backpacked. I can't say what makes it magical on a public forum, but I'll bring some. Let's just say that it leaves you with a nice "tingle" after a shower. And, if you ever get bored, you can read his religous ramblings on the packaging. Interesting stuff.