If you're on a thrifty mission, your best bet is this Hinge Tank. It's a terrific item, while not very costly. Another strong contender for your wardrobe is this Yummie by Heather Thomson Tank. While the price of this product is competitive, it will surely attract a lot of attention. You might also want to consider this Halogen 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, we've got your back with this Helmut Lang Tank. This piece is bound to become a total wardrobe staple. It's also worth looking at this Pam & Gela Tank. This product is extremely popular and, just as importantly, not too pricey. Alternatively, opting for this Eileen Fisher Tank is a good choice as well!