Before iTunes supported the "composer" tag I made extensive use of the "Comments" field. "Track" is always the name of the movement, "Album" the whole work -- but I realize that's not entirely logical, and is particularly annoying when the piece comes from a theme album of some kind, where you actually do want to save the specific name. Now I use the "Comments" field for that, but it's just silly that I have to do that. (Now that iTunes supports the "Group" tag, which is supposed to be for just this, I could move all the album tags into the group tags, but I also play the MP3s on my Archos Jukebox, which is lucky to support any ID3 data at all and laughs mockingly when I timidly present it with any but the bare minimum of tags.)