This is an idea that I heard from a guildy and most seemed to like.
A guild bank where anyone could put an item, and fellow guildys could take those items from the guild bank and use them, but 30 mins after they log out it ends up back in the guild bank for someone else to use.
You could have say a Superior Potency item for someone that doesn't have one, they could use it untell they get there own.
As far as management goes, that would be up to the guild leader to take items out.
Also a guild calendar would be cool, something you could pop open and set dates and times for raids. I mean we have a message of the day, but this might keep track of calendar days.
Also this is an idea me and my wife had.
When someone in a guild is part of a party that beats a raid, the raid bosses head appears on there guild houses wall. This would prob. be something that you could turn on and off as I imagine not everyone wants raid heads on there guild house walls.
Also the plaque colors could be maybe silver for normal, gold for hard, and platinum for elite.
Also you could click on the head and a list would pop up with the names of everyone that has done the raid, I know this last one is a bit of a stretch.