If you're in a thrifty mode, your best bet is this Chan Luu Necklace. It's a great item, while not very pricey. Another strong contender for your wardrobe is this Shashi Necklace. While the price of this piece is rather reasonable, it will surely attract a lot of attention.
If you're looking at it like an investment piece, then what you're looking for is this Loewe Necklace. It's more expensive but worth your money. Why not take a look at this Lanvin Necklace too? Expensive, but worth every penny.