Well, it depends on what you want to attach. There are some addons that will let you right-click and cast a mage portal and one that shows your tradeskill buttons. So really need a better idea of what you're trying to do in order to make any suggestions. :)
Jesamyn: I have this bar with stuff that doesn't have to be visible and easy to click; Hearthstone, Tailoring, First Aid, Create Bonfire, Beast Training (hunter) and a few more. A dropdown with the icons or simply the icons on FuBar would be nice.
Harwel: I'll try it. Though PerformanceFu can also show all your addons' usage ;)
TCGtradeskillsFu will definitely cover first aid, tailoring, cooking, so on. TransporterFu will cover the hearthstone as well as mounts. I have no idea about Beast Trainer, since I haven't played a hunter.