Here's a nice website with a large list of ID3 tags (not too sure if every single one is included):
http://www.sno.phy.queensu.ca/~phil/exi ... s/ID3.html
Steven, how does this compare to what you have? a06lp, the 'Mood' tag is the TMOO ID found int ID3 v2.4 tags. I wonder if MediaMonkey changed the naming (for whatever reason), and that is the tag you were after from the start?
Anyways, as said, pretty cool site, worth having a look.
Hope this helps
David