If you're not planning on spending much, these Urban Outfitters Sunglasses will fit the bill. It's a fail-safe choice, while not very expensive. Another strong contender for your wardrobe is these Cat Eye Sunglasses. While the price of this piece is competitive, it will definitely attract a lot of attention. You may also want to look at these Quay Sunglasses. This item is not expensive either, but it will make a difference in your wardrobe.
If you're looking for something in between pricewise, why not look at these Ray-Ban Sunglasses. While the price is very reasonable, this product is an easy wardrobe update.