Don't know why, but for some reason I always feel that my UI is messy/cluttered/taking up too much screen space.
Here it is.
Addons:
Xperl - for Player/Target/ToT frames
Grid - Raid frames
Quartz - Cast bar
Powerauras Classic - Icons for cooldowns
NeedToKnow - ICD bars
Dominos - Action bars (At the lower left.)
Ora3 - Maintank bars
The only thing I can think of to help is shrinking things down, which I've done with Grid already (not shown in screenshot).