Update: The slimmer 250GB PS3 model (in black) will be available in the U.S. on September 25 for $269, bundled with the "Game of the Year" edition of Uncharted 3 and a voucher for $30 worth of content in the free-to-play shooter Dust 514, according to the PlayStation Blog. A non-bundled version of the new 250GB console will be priced at $249 eventually; however, a Sony press release notes that only bundles "will become available at launch timing."
The 500GB model will launch for $299 on October 30. The blog also revealed a special, limited edition Assassin's Creed 3 bundle was in the works, but did not announce price. In a press release, Sony noted that Japan will get the white model and that "other regions and countries will follow."