Fubar is one of those addons that I didn't know I needed until I tried it out. It lets you display information in a bar at the top and/or bottom of the screen -- all the numbers and meters that you want to always have handy, without having to click on anything or hover your mouse for tooltips. Fubar itself provides a framework for the Fubar modules (downloaded seperately) to display this information for you -- anything from your durability to your current experience (with rest) to the time of day (both in your time zone and on your server).

I personally find one of its most useful features to be that it can show you how many of your guild mates and friends are online at any given moment, then let you hover your mouse over the number to see a tooltip list, with clickable names for whispers or invitations, just like a regular IM program.

To be honest, I actually tried out its competitor, Titan Panel, long before I had heard of Fubar, and then switched to Fubar because it feels more flexible and lighter on my system. Fubar is made with Ace, which usually helps addons feel smoother somehow; the difference between Fubar and Titan is what made me go looking for other Ace addons. Also, the other thing I love about it... is that it's called "Fubar!" and most of its companion module addons end in "fu", as in "QuestsFu" and "MoneyFu!" I just love my addons with a extra helping of humor sauce.