If you're not planning on spending much, this Adriana Orsini Pendant will fit the bill. It's a foolproof choice, while not very expensive. Another nice option is this Alexis Bittar Pendant. While the price is rather reasonable, be sure that this item will become a wonderful addition to your wardrobe. Or you can opt for this Vita Fede Pendant. This item has all the potential to become a powerful player in your wardrobe.
If you want to treat yourself, then what you're looking for is this John Hardy Pendant. It's more expensive but worth your money. While you're at it, also have a look at this David Yurman Pendant. Yes, this item is expensive, but it does not mean it's not worth it. Also look at this Kwiat Pendant. You won't regret the money spent!