Just in response to an earlier Mrrzy post:
the question was posed,
where to end Movie 2 and begin Movie 3?

The ultimate decision
is one of the few things of which I approve.

"The Desolation of Smaug,"   movie 2,
ended with the great wyrm Smaug
leaving the Mountain and heading into the open air
for the first time in how long? Anyway,
Smaug's death is imminent,
but first he has some humans to kill.

I think it fitting, actually,
that movie 3, The Battle of Five Armies,
begins with Smaug visiting ruin upon Lake Town,
and proceeds from there
to all-out war.