Did you know that Diet Coke can be used, along with Sprite, to make the soda visual-equivalent of a Black and Tan? It's fun for the whole family! First, pour (or preferably, use a soda tap) regular Sprite to about the halfway point in your glass. Then, carefully pour (or fill) the remainder of the glass with Diet Coke, along the inside edge thereof.
The end result will be a glass that has the clear Sprite at the bottom, with the Diet Coke floating atop.
The principle behind this is similar to the reason why diet sodas sometimes float in coolers and regular sodas sink: Nutrasweet is very potent, so the manufacturers only need to add a little bit to the syrup to get that sweet flavour, whereas regular sodas contain a lot of heavy sugars. Thus, having a higher portion of its contents being water-based, the diet cola will sometimes float in a bin of ice water, and the regular soda will sink.