Few things reveal a man's character better than what he has on his walls. Street signs command respect but that respect is based on the sign's overall quality. For example, a "No Parking" sign is a whole lot different than an Augusta National "No Women's Bathrooms" sign. Beer posters are fine, but be weary of generic ones.
I think the key to room decor is accessories, not posters. Think old hockey sticks, boxers that your roommate peed, previous write-ups, old volcano bags, christmas lights (are those kosher with ResChafe?), that sort of thing. Not to knock posters, there are obviously plenty of gems out there, but accessories generally bring a story along with them.
Finishing the perfect decoration job on a room gives a man a sense of accomplishment rivaled by few others. If you've got a set up around BC you think we might wanna take a look at, send a pic to firstname.lastname@example.org.