CodePen - A front end web development playground.
paste.ulvis.net - Add paste
JSFiddle - Test your JavaScript, CSS, HTML or CoffeeScript online with JSFiddle code editor.
Pastebin.com - Pastebin.com is a website where you can store text for a certain period of time.
Liveweave - Liveweave is a HTML5, CSS3 & JavaScript playground for web designers and developers
GitHub Gist - Gist is a simple way to share snippets and pastes with others.