It seems like the majority of low-carbers are using a relatively new sweetener called Splenda. It is available in most supermarkets now, or online if you can't find it locally.

It tastes very much like sugar, has no aftertaste to me (although my friends notice a tiny one.) It is made from sugar but is safe for diabetics because it is processed differently.

It is also referred to as "sucralose." Many diet soft drinks (such as Diet Rite, Waist Watcher, etc.) are now starting to use it (and sugar-free Jolly Rancher gel/jello cups are made with Splenda now too!)