This is my dental floss of choice. It is very bare bones, but made of excellent material. Like the wheel, this is something that has likely reached the peak of its effectiveness and will not, cannot, be improved upon.
Other types of floss are all flawed for different reasons. Cheap generic flosses are unpleasant and even painful. Some flosses are flat and tape-like - these flosses are difficult to grip, and though they glide nicely between teeth, they lack the ability to "scrape" sides of teeth and thoroughly remove waste material. Other flosses I've encountered resemble a soft, rope-like material. I'm not exactly sure what to say about this type of floss other than it sucks. Rope+mouth=not good.
Johnson & Johnson Reach Mint Waxed Dental Floss is widely available and is around three dollars for fifty-five yards.