If you'd rather not spend much, this J.Crew Necklace will fit the bill. It's a popular choice, while not very expensive. Another strong contender for your wardrobe is this J.Crew Pendant. While the price of this product is not very high, it will certainly attract a lot of attention.
For something in the middle of the price range, consider this J.Crew Ring. While the price is very reasonable, this product is an easy wardrobe update.