It might be unfair to follow up the JSBin update with this beauty; but the functionality and UX of Codepen makes things like jsfiddle or JSBin look like the minor leagues. Codepen really nails this, and features all things that I told myself I’d need from an online editor/snippet-share site. Not only can I favorite/follow/comment every post, I can browse the stuff other people love. DSL/precompiler flavors include SASS/SCSS and HAML, there are lots of tasty keyboard shortcuts to manage window panels and utilities like JSLint. Adding external stylesheets and script files is a breeze, and the editor options include choosing from some hosted fonts and many of the most popular syntax themes.
Also, it’s built with Ruby on Rails and can use GitHub for authentication.
Oh, and it’s only in Beta. Can’t wait to see what the v1 release will include.