Well, today Ubisoft confirmed it would come to the 360.
http://xbox360.ign.com/articles/729/729877p1.html
This is great news for 360 owners. This game looks very good indeed. I don't quite get all of the PS3 exclusive hyping that was done, and why they would announce for the 360 now. Doesn't seem to make sense....Ubisoft sent us word that Assassin's Creed, the next-gen title that wowed everyone and their mother at this year's E3, is indeed coming to Xbox 360. The latest news confirms what has been rumored for so long and comes hot on the heels of news earlier this week that the game would be coming to the PC. Assassin's Creed on Xbox 360 will be released to coincide with the Playstation 3 version in the first quarter of 2007. The title is being developed by Ubisoft's Montreal team, the same group that has put out gems such as Tom Clancy's Splinter Cell and Prince of Persia: The Sands of Time
--Raz.