The seven rings of the dwarfs are lost or consumed by dragons.
The ancient evil overlord "of whom Sauron was but a servant" is of course Morgoth.
Shelob in fact was not exiled. She is believed to be one of the last descendants of Ungolianth, who together with the above mentioned Morgoth killed the two trees of Valinor and took the Silmarils in the Elder Days and was exiled for this.
The Witchking of Angmar in the Third Age served Sauron as captain of the Ringwraiths.
These questions are mostly taken from the Silmarillion, which is agreat book by the way as it gives the Lord of the Ring a much bigger frame. I believe only if you have read the Silmarillion you can fully appreciate the aspects of the fading of the elves and the Numenoreans and the real "historical" importance of the story.
christian (you're too late, jsbothe!