I guess this is the most valuable -- ivory 100, 2" wide. (Except for a large ivory and sterling dealers' chip; don't have a photo of it. It is on page 363 of Seymour's book (both sides).)
And here are nice mother-of-pearls -- part of a large cased set of 100's of pearls I own:http://www.megsinet.com/wally/Robert/rfmop5.jpg