Even though it has some extra features I like using Mage Nuggets for my Boomkin's Eclipse.
It's very customizable, take some time to look through the options, but it gives a small window packed with information.
My favorite feature is that it has a Wrath icon for when you need to spam Wrath and a Starfire icon for Starfire spamming which makes it easy if you're managing a lot of things.
It also plays the A-Team song when your Treants are out. :P
Gershuun @ Borean Tundra US - Interface & Macros Moderator
I use balance power tracker. Its moveable (and scaleable I think), but the thing I like is that it "predicts" what your eclipse power is at while casting, or wrath is in flight, so you can more easily start casting the other nuke before eclipse actually happens.