For those of you who group, raid, and otherwise hang out with your guild, here's some pretty cool news for you. Tigole has said over on the Beta Suggestion Forms that the dev team is very interested in the idea of guild achievements, and does plan to visit them in the future.
It's a small tidbit, but it's enough to get the old wheels turning. The most obvious achievements will probably revolve around dungeons and raids. Get X% of your guild through a certain dungeon, perhaps, or finish the dungeon in an all-guild group. We might also see accomplishments for getting a certain amount of guild members their tier sets or legendary weapons.