I am not sure how often you can use this, but its still is a cool trick. By placing the following line (data:text/html, <html contenteditable>) of code into the address bar it will turn your browser window into a notepad.
I have tested this in the latest releases of Google Chrome and Mozilla Firefox and it worked fine. It does not work in Internet Explorer, I have tested both versions 9 and 10.
For more information about this trick.