My guild has a few sayings (most of which have already sneaked into Guildwatch), though my personal favorite is simply yelling "Shaman Power!" when a Shaman in guild gets a nice drop or does something spectacular. Not nearly as catchy as Anteia's examples, though.
Has your guild built up your own jargon or sayings? When a group of people are placed in situations like this, it's almost unavoidable that they'd build up their own meanings and words among each other. What are some good sayings and phrases that your guild uses ingame?