I just added to my wish list - Creative illustration by Andrew Loomis. Just by flipping through it you can see that it gets so deep into composition like no other book I ever seen. Also, there is a free scan on the web, poor scan, but legal :)
Also do you have some favourite reference books? For example I just bought "Racinet: Complete Costume History" for references on historical clothing. Since it was really hard to google some good 12th century clothing references and be sure it is somewhat accurate.