Here is a very good set of drills for clearing out at ruck time.
We should definitely be training on some of this, though the current drills (Joffa's one) are doing a good job of getting people focused.
Running Ruck - Rapid Maul
As per an email I sent today, the other thing I would like to see - given our big size advantage and speed - is the "Running Ruck" where a ball carrier stays on his feet long enough for support to rip and pull the ball back to the rear of the maul. The defense will pull/tackle the front man in the maul and the others have to have their heads up (low body position though!) to be ready to un-bind and splinter off. Probably after 2-3 phases, the man with the ball will easily break through the defensive line, meaning he can offload to the others who will chase in support. The defense will struggle to contain this if done properly.
Pick & Go
Otherwise, our classic "Pick and Go" is always a threat. The only issue is that if 2nd XV members are on the field, some have to be appointed ball carriers. If no-one is "Picking", we won't "Go" anywhere!