I just became aware of some really cool Flex UI components. Maybe they've been out awhile, so I apologize if folks have seen these already. Anyhow, Doug McCune has some really cool UI components including vertical and horizontal sliders, various menu widgets, vertical and horizontal accordions, and a super tab navigator.

The sliders can be real handy if you need them. Especially if you are considering building your own in Flash, cause it's not easy. I also like how the alternative scrolling pane works though I can't think of a real good use for the component save an interface with miniscule screen real estate. While all of these are useful and slick, the super tab navigator component is my favorite. It looks and functions similar to Firefox's tabs allowing you to close individual tabs by clicking a close button and drag tabs around to new positions. Doug took it even further allowing you to access open tabs using a drop-down control (one of his other components by the way).

You can check them all out here:
http://dougmccune.com/flexlib/keynote/