I found this forumla in a guitar book. I'm assuming it's basic on harmony theory. I find it quite useful. maybe some of my friends at talkbass might find it useful too.
- An I chord can change to any other chord.
- An II chord can change to any other chord except I.
- An III chord can change to any other chord except I or VII.
- An IV chord can change to any other chord.
- An V chord can change to any other chord expect II or VII.
- An VI chord can change to any other chord expect I or VII.
- An VII chord can change to any other chord expect the II or IV.
Edit: The Guitar Handbook by Ralph Denyer