So far, the most useful Shout I've found for such situations is the "slow time" - if I can actually get near the dragon during the few seconds it's landed, I can at least extend the period it's on the ground.
I have destruction's "impact" perk. Some people talk about stagger-locking dragons, but in my experience (perhaps I just have the timing wrong), they always seem to fly off even if I've just hit them with a dual-cast firebolt/ice spike/lightning bolt. They sometimes get stunned, but more often than not, they seem to just shrug it off and go fly away.
