I saw a movie a few weeks ago called Fat, Sick, and Nearly Dead. It is a true story of a man from Australia who comes to the US and goes on a juice fast. He ends up losing a lot of weight. If you haven't seen it, it is very inspiring (kind of like The Biggest Loser). I recommend it.
Interestingly enough, the guy in the picture above is star of the film and has a site where you can learn about juice fasting. There is a lot of information and a few different types that people can do. The site is: http://shop.jointhereboot.com/
Now, I have tried these in the past and found that they only make me crave bad food more. However, I've heard that if you keep going, it gets easier.