I'm a longtime fan of David Shillinglaw's art. It's impossible not to be. He's got great instinct when it comes to letters, layers, shapes and colors, and wait until you see what he can do on a concrete wall.
If you've never taken a marker or paint brush to a wall, get off your butt and make it happen this weekend. You must, if simply for the challenge when it comes to size and scale. It's by far my favorite canvas and no one does it better than David.
Below are some of my favorite of his images (including a video of his process).