I originally found ElvUI in the comments a couple weeks ago in this very column, at the time I had been working on a letter for a call for help, but once I found this I stopped cause I found what I was looking for. As a Balance Druid I always had trouble with UIs, either they cost an arm and a leg in resources (me being one of those who do have issues) or spread everything out on the screen so much that I couldn't focus. This gave me that and something nice extra that I'm kinda surprised you didn't mention, this UI has an option to color the theme according to your class colors. It's just making the thin line orange on my Druid or purple on my Warlock but it's effective. The built in skinning is great, as is the modual I found that would skin DBM, it makes the overall UI come together, makes each addon feel like it's supposed to be there.

Here is what I did with this addon.
http://i114.photobucket.com/albums/n243/RoboDuckyX/WoWScrnShot_111210_203640.jpg
Also you can't really see it in this pic here but I moved the DBM allerts over to the quest tracker area to clear out the top of the screen. With this I have finally been able to keep everything to a nice "U" shape, well... maybe more like a "W", but the parts of the screen I most want clear are clear. For me this UI has been a winner and will be what I use going into Cataclysm.