Here is one for DD, though I get the feeling you probably know about it already.

http://www.hoax-slayer.com/russian-K7-heavy-bomber.shtml

And here is the largest plane in the world in 1934, the famous Maxim Gorky:

http://flyghistoria.se/tupolev_ant20E.html

A little more sucessful this one, I belive that this was the first aircraft to be used to drop paratroops as well.

They would exit the aircraft at the top and literally slide down the wing and off ito space 

I'm not sure that turret would really have been put on the aircraft it look like it's off a battleship to me, fire that airbourne and you have formation flying kindling!!!!!

I think those ones are CGI, if you look at the article I posted you can see although large the plane isn't as big as in the ones posted by Data.