Somehow a Taiwanese Web site got its hands on all the posters for the Left 4 Dead 2 - and if these are real, that means the names of the final two are known: "Dead Center" and "Hard Rain."
Dead Center - "Prices Aren't the Only Things Getting Slashed" - appears to be a shopping mall setting. Has that ever been done with zombies? Hard Rain - "Come Hell and High Water" - looks to be set in some kind of refinery and the knee deep water suggests what you'll be slogging through in it. The full size posters are after the text.
I've emailed Doug Lombardi to ask if Valve would like to comment. A tipster told us that an L4D2 playtester had seen these and pronounced them accurate. But if Team Fortress 2 has taught us anything, there are plenty of artists out there who love to make up stuff using Valve IP.
Are Dead centre & Hard Rain the Last Two L4D2 Campaigns? [Evil Avatar, thanks Jim and David]