The Extreme Ultralight is 34" x 28" and weighs under 3 ounces, so you can still carry a towel large enough for swimming or bathing! They also pack into very small spaces.
If you are a minimalists, Discovery Trekking Outfitters makes an even smaller version . Weighing approx. 1.3 oz, it's approx. 19" square, and serves as towel, neck, or headgear.