My girlfriend in London has two delightful baby boys and she swears by the amber teething necklaces that they both wear to relieve their teething symptoms. As amber is a resin, not a stone, it is purported to have healing properties, especially when in contact with the warmth of baby's skin. The string is weak enough to break if caught on something, but each bead should be strung individually so that only one should fall off if broken.
Meredith Marshall of Amber Bebe provides a detailed overview of the benefits of amber teething necklaces on Mumzone. I think they're worth a go - especially if they provide teething relief - and they look pretty cool too.