If you are on a budget, your best bet is this Vince Tank. It's a great item, while not very pricey. Another nice option is this Nike Tank. While the price is competitive, be sure that this product will become a wonderful addition to your wardrobe. You might also want to consider this Express Tank. The price is very reasonable, but the effect on your wardrobe will be pretty fantastic.
If you're looking at it like an investment piece, then what you're looking for is this Victoria Beckham Tank. It's more expensive but worth your money. Another product we're drooling over is this Emilio Pucci Tank. It's pricey but you get what you pay for.