Sin City 2 has been confirmed to start shooting in January (Sin City 3 sometime afterwards), but that is old news; Sin City 2 storyline, however, that is a brand new annoucement/
Sin City 2 will follow the story line of A Dame To Kill For which follows Dwight (Clive Owen from the movies), and will feature minor return parts for Shellie the Barmaid (Brittany Murphey...yes!), Marv (Mickey Rourke), and Nancy Callahan (Jessica Alba...another yes!), and heavily features Dwight ( as mentioned above), Miho (the Japanese samurai from Sin City 1; Devon Aoki), and Manute (I forget the actors name, but he was the guy with the gold eye) as well as a whole host of new characters, including Ava, and The Colonel.
A synopsis from IMDb.Com -
It's one of those hot nights, dry and windless. The kind that makes people do sweaty, secret things. Dwight's thinking of all they ways he's screwed up and what he'd give for one clear chance to wipe the slate clean, to dig his way out of the numb gray hell that is his life. And he'd give anything. Just to cut loose. Just to feel the fire. One more time.
I can't wait!