I've been healing on my pally for a few months, but when I was raid healing on my druid, I'll admit that I didn't pay much attention to my pally's cooldowns and extra buttons. I wasn't a good holy pally.
Now that she's getting more play time, I'm actually using my cooldowns more often.
My favorite has been nicknamed "the Time Out Button".
It started when I was in a ZA with my husband. He got too close to the mobs to hex, pulled, so I Hand of Protection'ed him with 1k hp until I could get the tank stabilized, then I healed him back up.
While I have used it to protect myself from healing aggro, I really hadn't thought about using it on the dps before (like I said, I'm still learning the holy pally). My first thought was that it would be fine for casters, who could continue to dps.
Then I was in another heroic (GB, for variety) and the dps DK kept pulling aggro. I was yelling at him through the screen to stop that, so the next time I cast HoP, which kept him from being able to dps for several seconds.
As a lesson, I think it worked... he stopped pulling aggro, but I didn't have to let him die and slow the group (I am totally that healer). It said "I see what you're doing and you should stop" without punishing everyone else. It's a lot more obvious than Hand of Salvation (and more effective to get the mob(s) back on the tank).
Obviously, in a raid I save this button for it's intended purpose, but when running 5 mans with badly behaved dps, I really like having my time out button!