Bonfire of the Vanities is the upcoming DLC due for release sometime this month, unless things have changed since its announcement.
Sequence 13: Bonfire of the Vanities
End of February - $4.99
A must for Assassin's fans, Assassin's Creed II Sequence 13: Bonfire of the Vanities continues to expand the addictive AC2 universe. Work with Machiavelli to free the city of Florence from the grip of the mad monk Savonarola by targeting influential citizens under his control.
Battle, sneak and free-run your way through more than ten challenging new memories. Discover a new district of Florence, and utilize Ezio's brand new move: the spring-jump.
Both DLC packs are said to represent a pair of sequences that fill in the gaps in Assassin's Creed II's main story. So now you can actually finish it properly.