From: http://mcdlr.com/
See it live at: http://mcdlr.com/8/
Just a list of commonly used HTML entities with the proper code in decimal entity notation.
I uploaded this a long time ago but did not consider it worthy enough for it to be shown here. But you know what? I use it all the time!
If it's so useful for me, it's probably gonna be useful for more people, I guess :)