I personally love the buff from the shamans in Utgarde Pinnacle. Making you into a spiritual wolf hitting for 5-6k white damage every 0,5 seconds.
The Fireball buff from the big guys in HoO is really fun aswell. I love to take it before the first boss and just jump down and kill all the snakes, then have a priest grip you up Doing 40k dps at that fight is phun