I imagine most WoW players have messed around with UI Mods at some point or another. I decided to try redesigning my interface since I have not kept up with the latest mods since about November sometime last year. I was pleasantly surprised by how much they have improved since that time. In particular, the mods based on Ace2 are very impressive. Any mod based on Ace2 automatically has profile support, GUI configuration, extensive command-line interface, etc.
So, after messing around and trying a bunch of different mods, here are the mods I decided to use. Note that about 80% of them are Ace2 mods (www.wowace.com).
FuBar and FuBar accessories