A sweepstakes promotion by GameStop and Bethesda Softworks says the upcoming FPS Brink will be available September 7. The promo also shows some box art for the game but it's unlikely that's the final version.
Yesterday afternoon the Bethesda Blog posted a link to the Brink GameStop sweeps, which is pretty sweet on its own. (55-inch LED TV, 5.1 surround sound home entertainment system, your choice of PS3 or 360.) The page also says "Available 9.7.2010." Given that the rules state that Bethesda is the sponsor of the sweepstakes, it stands to reason someone there had approval of this marketing material, so it's not like GameStop jumped the gun or erroneously plugged in an availability date, as is sometimes the case. The preorder page also lists Brink for Sept. 7. Sounds good to me.