Left For Dead coming to DS?
The Australian Classification Board seems to think so

According to a recent listing on the Australian Classification Board website (picked up by Cubed3), upcoming Valve-developed survival horror game Left 4 Dead could be coming to DS.
The game has previously been confirmed for Xbox 360 and PC but not for handheld. It's not exactly an obvious fit for DS either - being a blood-soaked PC survival horror game and all - but at least the game's co-operative elements could work over wi-fi or local wireless on DS. Still, we're going to reserve judgement on whether this is fact or someone's typo until we get some more official confirmation.
Left 4 Dead is the latest game in development by Valve - makers of Portal, Half-Life and Counter-Strike. It promises to re-define the co-operative genre in a similar way Counter-Strike did the multiplayer one. The game features four survivors struggling against swarms of zombies and 'Boss infected' mutants. See what I mean about not being the likeliest game to be adapted for DS?
Still, if it's confirmed we'll be sure to let you know.