Common knowledge but if you have Morbidity (Unholy talent: Increases the damage and healing of death coil by 15% and reduces the cooldown on Death and Decay by 15 sec). You can spam Death and Decay and Horn of Winter until you have full runic power before any boss fight.
Is nice for Blood or Unholy DK's who can get an early Deathcoil off as they are running in and also a Unholy Blight for that extra diesease damage at the start without having to waste a GCD :P