I think a list of all the available guilds in game is a amazing suggestion! This way you know what guilds there are to choose from, you can send a "guild join" message to them so Guild owners can accept or reject players who want to join them.
Following on from this, you could find a player whose guild you like the look of, and press to button to send a guild join request.

Please tell me what you think of these and if you would use it!