We knew Assassin's Creed II was getting downloadable content and Ubisoft even announced the names of the expansions -- Battle of Forli and Bonfire of the Vanities -- but Ubisoft has released more details today, including a price breakdown (it's more reasonable than you think).
Battle of Forli will be released in late January, and consists of six memories (read: missions) that involve Ezio being wrapped up with Machiavelli and Caterina Sforza as they defeat the Orsi brothers. Participating will cost you $3.99. Bonfire of the Vanities will arrive not long after, sometime in February, and include ten missions inside Florence, a new move (the "spring jump") and cost $4.99. You'll be tasked with taking out the monk Savonarola to finish the job.
These additions are the two "corrupted" memories you may have noticed in the game.