If you're on a thrifty budget, this J.Crew Hat will fit the bill. It's a great choice, while not very expensive. Another savvy option is this Opening Ceremony Hat. While the price is competitive, be sure that this piece will become a valuable addition to your wardrobe.
If you can afford to splurge, then you absolutely must check out this Knitted Hat. This product seems expensive, but it's top quality. While you're at it, also have a look at this Beanie. Yes, this item is expensive, but it does not mean it's not worth it.