If these have been said before, please don't be harsh :/ These are useful ideas.

1. Message Board.
I find contacting a guild about something going on within the guild is hard and so a message board would be handy. Open to all members to post but, comments and restrictions can be placed by the owner of the guild about who can post messages etc.

2. Weapon Demonstration.
The option to use weapons in guild halls. Eg. Demonstrating weapons etc to fellow guild mates.

3. Battle Simulation room.
A fun room where guild mates can get together and test their metal. The room spawns any desired monsters (which drop nothing) and when Knights die they must be revived by other guild mates but, this costs nothing.

4. Rank drop down list.
When I promote someone another additional tweak would be to have all the ranks drop down in a drop-down list. This would be more efficent then cluttering the chat with:
Kinggobi has been promoted to member!
Kinggobi has been promoted to veteran!

5. Distinguishable Guild Members.
Guild members show up on mini-map in haven under the guise of a "G" (this could be implemented for friends as well)

6. Community Chest
A chest in which more experienced guild members can donate crowns to the guild and less experienced members can obtain a quota once a week (quota being set by Guild Master) of crowns.

7. A Handy Message
A handy message to new member saying "You've joined "insertnamehere" to speak in guild chat type /guild before your sentence"