Bumbershoot? Okay, it's an annual arts festival in Seattle that started out as a music fest, but now includes a gallery (and sale) of posters from around the country. Check out Flatstock. The images above are all from Seattle shops (and not the ubiquitous Modern Dog, Jeff Kleinsmith, or the young hipsters from Asterik Studio), but the show includes designers from around the continent (sadly, Denver is not on the list).
Links for the designers represented above: