Be wary of these. They are supposed to trim calories, but may be dangerous in more significant ways! If you want to trim calories, help yourself to the full-sugar drinks (not diet brands) and drink less of them!
Aspartame (Nutrasweet & Equal). The artificial sweetener used in many diet sodas has long been rumored to cause problems, but a definitive study did not appear until 2005 which found significant increases in lymphoma and leukemia amongst rats fed aspartame. A 2006 study by the National Cancer Institute (NCI) found no link between aspartame and cancer; however, that study only studied people aged 50-69, not people across their entire lifespans.
Saccharin (Sweet'N Low). Animal studies have found it causes cancer of the urinary bladder, uterus, ovaries, skin, blood vessels, and other organs.
Sucralose (Splenda) has a disputed record of safety. Some argue that its "natural" chlorine bonds are safe and that the no-calorie substance has little which is absorbed by the body. Others claim that too much chlorine is unsafe, that rats have shown adverse effects from sucralose, and that long-term effects studies on humans simply have not been completed, a history very similar to aspartame. Read here about effects pro (http://www.sucralose.org/facts.html) and con (http://www.splendaexposed.com).
Stevia (Truvia, PureVia, SweetLead). This is a new (2008) product for the US. Cargill, Wisdom Natural, & Whole Earth are putting it on tables and Coke and Pepsi plan to put it in soft drinks. However, while the FDA has called it GRAS (Generally Recognized as Safe), they did so because the companies said so. In other words, because it's an additive and not a food, the FDA approval is not required!). The Center for Science in the Public Interest and Univ. of CA, the active ingredients have caused mutations, chromosome damage, or DNA breakage. Only half of the active ingredients have so far been animal-tested, and then only in a single species (when two are FDA required). In short, the increased risk of cancer is simply unknown. (http://www.nutritionaction.org/stevia)