Stevia alone is pretty awful, very bitter aftertaste. But there are some new stevia derivates that aim to remove the bitterness and turn it into an acceptable sugar substitute. Pepsi has developed one, and the Coca-Cola Company, with Cargill, have recently developed Truvia (http://en.wikipedia.org/wiki/Truvia), which is already being used in some of Coca-Cola's beverages. You can buy it in packets for home use. So far, TruVia is the best-tasting artificial sweetener I have come across. Much better than aspartame, sucralose etc. No bitterness to speak of.

Another natural sweetener called erythritol (http://en.wikipedia.org/wiki/Erythritol) is also very good. Unlike stevia, I believe it works on its own, with no modifications required to remove bitterness etc.