TERA is running an open beta until 11:59pm Pacific. To sign up, just go to your En Masse account page (it's free to sign up) and add the code TERABETA. It's a fairly solid MMO, and worth checking out. I'm still not sold on buying it for full price at launch, but maybe playing for a bit more will change my mind.
While at PAX, the developers gave me a number of keys to hand out that grant access to the beta and a Regal Frost Lion mount. This mount is exclusive to the collector's edition of the game -- unless you use one of these codes, that is.
You won't be able to use the mount unless you buy the game, so please don't just grab one if you aren't planning on buying it. Post in the comments if you take one, so everyone doesn't sit here trying the same code all day.