Originally Posted by Xejin

Bartender, Pitbull, FuBar for starters.

Quartz for a great casting bar.

Morganti's Buffbars for great buff/debuff icons/bars/timers.

That's how I built my UI.

The really nice thing about all of these addons is that they autodetect for class. Meaning you can make class specific UI's that work across all characters of the same class.