Unregistered

Hi.
I am looking for a painting I have seen a few times before, so I know it is kind of famous. I last saw it in the Tate Modern about a year ago, and it was also the basis of the homepage to 'Qwyzzle' (if anyone knows what that is).
It depicts a man sleeping under a moon, and as far as I can remember, a brown thought bubble with a few items floating around in it including a hat, a candle, and some others.
I would appreciate it if someone could tell me either the name of the painting, or the painter, etc.
Thanks
Josh