I did a
fairly detailed article on the history of airships on my blog recently. One interesting fact I discovered:
the world's supply of helium is very limited, and is running low. If airships are to make a comeback, they'll have to find a way around that problem.
I agree with Maxor that airships are likely to be far more viable as a commercial heavy-lift platform than for military applications (with the exception of surveillance missions, which are a field unto themselves).