What spec? What your spec is would heavily influence what addons would comprise a good UI for you. As a healadin I use Bongos for action bar placement/control, Healbot for healing and similar things (cleansing, blessings, etc) and a few various other ones for raid information and reporting.
Healbot will get plenty of positive and negative feedback from other forum posters I'm sure, since personal preference seems to lead people in a few different directions (Healbot, Grid, a few others) But Healbot has seemed to take care of my healing needs...and I've successfully run everything short of 25man content as the main healer.