Though both are not ready for prime-time, jsFiddle currently appears to have more options than JS Bin. It can format code to make it more readable. Both of them help you build quick & dirty code samples using Frameworks like jQuery, while you are experimenting or building a prototype. Without having to sign-up, you can save your code & generate a public link for it. You can then send this link to others anywhere across the world to review or seek help with debugging.
(JS Bin - click on the image to view enlarged screen-shot)
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