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

I've seen it before 

One of the weird and wonderful large russian designs from between the wars, they did like em big.

Here is an article with a real photo, and if you read the article you will note it wasn't a good idea to fail with Stalin around!!!!

http://www.aviastar.org/air/russia/kalinin_k-7.php

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 

That K-7 Heavy Bomber has a fear factor of 10 in my book.  imagine the face on the enemy when that things start shooting 

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 don't know the authenticity of the third photo either.
I would think those cannons would actually rip apart that plane, Although I'm not an engineer.

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.