On another forum I lurk on a person had a very cool idea about a guild dontation and here I'm going to add my 2 cents to it.
Here's a quick summary of what was said:
A player may choose to donate and item to the Guild Donation Vault. This item can then be taken by other members of guild. However, this item cannot be sold or traded to anyone else outside of the guild. Should the person who borrowed the item leave the guild, the borrowed item would return the guild valut. Obviously this means implementing an item tracking system. In addition, the person who originally submitted the item has the option of recalling the item and will give the person who borrowed it a warning that in x amount of time the item will automatically leave their inventory and return the orginal owner.
Personally I think this a very cool idea but will probably be a pain to implement. I definately think there should be some sort if item valut where guild member can donate any extra gear they don't want.