Healbot is nice and I used it for about 6 months before switching to Clique and Grid.

With Clique, you assign spells to mouse clicks. Then when you click on a "target frame", that spell is cast on that target without you losing your current target. You can left-click, shift-left-click, alt-right-click, etc. You can also filter target frames for greater control (so clicking on a portrait uses the default, but clicking on a Grid box casts heal).

Grid is just a series of boxes that represents your party or raid. It's used by all the high end healers and is meant to be as simple and efficient as possible. I'm liking it quite a bit, but I can't figure out how to get it to show pets (I don't think it can).

Healbot is also nice, it's like a combination of Clique and Grid. The one thing that annoyed me is it is stuck in two modes, combat and non-combat. Whenever I wanted to assign a spell, I had to do it twice since I don't like trying to remember combat and non-combat modes.