Vuhdo(which is essentially the Healbot 2.0 with less bugs and better UI, customization and looks)
Skada
DBM
These 3 are essential for playing in raids for me as a healer. I don't really use Weakauras much because there's really not much it can do that can't be tracked by a properly set Vuhdo or DBM, and as a result feel it's highly overrated.