Gianni Rossi has created some amazing gig posters including this one for Justice. I'm also trying to get hold of a Daft Punk one he's designed to add to my collection. [EDIT: IF you contact Gianni he is selling numbered and signed 50x70cm (Around A1) prints for 25 Euros each and 8 Euros p&p. I've ordered Daft Punk on white and the Justice one above.] Also, whilst I'm on the subject of gig posters the aptly named gigposters.com has a great collection of errr... posters from gigs. They're not particularly hi-res but there are links to purchase some of them as prints and links to the designers website and email.
