In advance of the significant Lost Shores content update that's arriving next Friday, ArenaNet will be allowing existing GW2 players to invite up to three friends to play the game for free from the 15th to the 18th. Those invites will be made available on Monday. Note that in order to do this, you must have created an account before midnight on November 6th, and that account must be in good standing.
Anyone here thinking of trying to get more people hooked on Guild Wars 2? I may just float my invites out on Facebook.