A regular on a music forum I frequent wrote this nice web app and encouraged people to use it. It is theory that I am sure some of you know but might be helpful to somebody else, a web link, or teaching tool you might wish to use. Hal Leonard has published a cardboard and plastic booklet for decades that sort of does this but it is presented here in online, interactive form. Enjoy!

http://randscullard.com/CircleOfFifths
http://randscullard.com/CircleOfFifths/UserGuide.htm