Recently came upon an addon called OPie, and I have to say this is one of the most well-built, functional, and down-right sexy addons I've ever come across.
As per the official site's description:
OPie is a radial action-binding addon for World of Warcraft. The addon allows you to bind groups of infrequently used actions to a ring that appears when you trigger it using a hot key / mouse binding.
How exciting, right?
Videos, screenshots: OPie ï¿½ Gallery
Download: OPie ï¿½ Downloads (Currently in beta.)
However, even the videos/screenshots do not do this addon justice. Install it, login, and hit ALT-T (tradeskills) and ALT-R (raid markers) for a quick demo of how... amazing this is.
Interface Options -> Addons -> OPie for configuration. It's ready to go for almost (all?) classes, though.
It works off mouse gestures. You don't even have to click the abilities/items, just gesture towards them.
You can make custom rings, simply by clicking and dragging abilities, items, whatever into the options window. Change icon color hues, ring rotation, order. It's all there. Can also share/send rings ingame.
You can also have the ring show up at mouse location, choose to show cooldowns, dim the game screen, show rings only on certain characters or classes, and a few other things.