If you're not planning on spending much, your best bet is this Zella Tank. It's a fantastic piece, while not very costly. You might also want to take a look at this Soprano Tank. It's an item you're bound to love which also won't break the bank. You may also want to look at this Pleione Tank. This item is not expensive either, but it will make a difference in your wardrobe.
If you're looking for something in between pricewise, look no further than this Michael Stars Tank. This item doesn't cost the earth, but absolutely essential in your wardrobe. You might also be interested in this Elizabeth and James Tank. It's an attractive option both price and quality-wise. Take a look at this AG Jeans Tank too! Great value for your money.