Graphic design is an important part of game development, and one that is much more an art than a skill. As someone who appreciates great graphic design, both in and out of games, I was very impressed by the street art in East London that I was recently able to visit.
Jonesy, of who you can see some work here, in particular was very inspiring.
Another discovery was Bicicleta Sem Freio, a very colorful Brazilian collective which makes awesome murals.
I would highly recommend everyone to go and take a look at the street art for yourself!