ArenaNet's highly ambitious, story-driven MMO Guild Wars 2 is completely free for anyone to try in the coming week. Starting tomorrow at 12 am PDT (that's 8:00 in the morning over here), anyone and everyone can download and play the game free of charge. The free period ends at exactly the same time on October 2nd.
If you already have a trial account from previous trial periods, you're good to go, otherwise you'll need to create one. Details on how to do that, as well as download the game, can be found on the Guild Wars 2 blog.