My studio is pretty messy right now by my standards, but I found this site called Have Some Tea that has an amazing photography collection of artists studios including some that have me beat. You have to go to the second page to see the messy studio of all time, that of Francis Bacon. I love how he tests his paints out on the walls and even the outside of his door, the one that faces the hallway.
UPDATE: More great studio shots at
You Have Been Here Sometime.
Below, messy shoes with Pink and Green Furrows, 64x96 inches, pumice, dry pigment and gesso, 2009 by Vincent Romaniello.
