This one is 176 x 156 pegs, or 55 x 48.5 inches. I hope I don't need to explain this, but this is the cover of The Clash's 1979 album "London Calling". Paul Simonon is seconds away from obliterating that bass guitar.
I chose this because it is one of the greatest album covers I can think of, and the nice mix of mostly greyscale with a splash of color.
Nice one! I've been trying to think of a good album cover to do to go in my basement and since you've picked the best album of all time I'll haver to go and put my thinking cap on! Well done - it looks great.