If you'd rather not spend much, your best bet is this Kardashian Kollection Tank. It's a popular piece, while not very pricey. Another strong contender for your wardrobe is this Tank. While the price of this piece is rather reasonable, it will definitely attract a lot of attention. You might also want to consider this Bioworld Tank. The price is very reasonable, but the effect on your wardrobe will be pretty fantastic.
If you can afford to spend a little more, look no further than this McQ by Alexander McQueen Tank. This item doesn't cost a fortune, but absolutely invaluable in your wardrobe.