I was fortunate to see a live demonstration of vffiddle at Dreamforce by it's creator, Nate Lipke (thank you!). It is based off of jsfiddle, but works with Visualforce.
This is an excellent way for users to post workable code snippets on SFSE. When posting, try to keep the features being used in the code common to those in all orgs (e.g., Accounts, Contacts, etc.) to make it more likely that the code will run in anyone's org that runs the fiddle.