I got to check out The Black Keys, Cold War Kids and Radiohead (the lights and stage cams made their performance even more awesome) on the first day of Outside Lands, the first music festival in Golden Gate Park. The design is by the legendary Ames Bros. The website is really cool too, check it out for event photos and videos.
Another classic designer, Milton Glaser is one of the most respected and well-known American graphic designers, and is the creator of several infamous corporate identities as well as the "I <3 NY" logo. He has a range of works from paintings to simple polygonal shapes, but his most unique works are known for their excellent use of color and simplicity.
A few things for Bloc Party, one of my favorite live acts. Their flyers are just as enjoyable, and seem to be almost as random as their more recent music videos (Mercury, Flux?). Check out Jazz Feldy's piece that he did for Bloc Party's Melbourne show that I posted earlier.
From Budapest, City on Fire aka Daniel Pelaky aka Blue Buddha Design shows us how a good combination of simple elements can produce something beautiful if the layout is set up nicely. His pieces have an extra dimension with added depth in the backdrop or through employing retro textures and patterns.