The Fallout3 GotY is showing a release date of October 13 on Amazon. I have Fallout3, but I just started playing it. I was going to play through once without any addons or mods and then pick up the DLC (or SBC) disks until I read that the Mothership Zeta won't be released on disk.
The GotY edition will include Fallout3 and all 5 DLC addons and can be pre-ordered now for $49.99. That's only a few cents more than buying all 5 DLC from GFWL or the two DLC disks and Mothership Zeta from GFWL, and you get Fallout3 again. Even if already have Fallout3 or you do and you don't have any of the DLC yet, IMO the GotY edition is still a better deal just because it will all be bundled together. You can sell, trade or give away your old copy of Fallout3.
"You can either want something to be true, or you can want the truth. Pick one. - Mr. Diety