You sir, if you make this shine as well as jsfiddle, I want you to come into my house and take one of anything. While you're at it, partner up with this guy http://www.tsqltidy.com/ .
I've been meaning to add links to other useful SQL resources, such as that and http://dbdsgnr.appspot.com/. If you think of more ideas, I'd love to hear them - send me a message @sqlfiddle on twitter. Thanks!
Not really an SQL tool, but if you use a lot of SQL then maybe you need to apply DDL and procedures to various environments. I have been working on an installer to manage your DB schema using migration scripts - http://dbgeni.com
