A new Assasin's Creed is said to be released this year or maybe between April 2010 or March 2011 which is Ubisoft's next fiscal year. The new game will include online multiplayer which is confirmed as the first of the franchise to include multiplayer.

"The 2010-11 fiscal year will see a greater number of franchise releases than in 2009-10, including Tom Clancy's Splinter Cell Conviction, a new game in the Tom Clancy's Ghost Recon series, Prince of Persia The Forgotten Sands, Driver, Raving Rabbids 4 and a new episode of Assassin's Creed, which will be the first in the series to have an online multiplayer mode," the company said.

I've been reading around and a few people think this is going to be an online spin-off.