I have two Left 4 Dead badfic to report:

"Life Undead" by honored cur. It is located at http://www.fanfiction.net/s/5783946/1/LifeUndead. Rated T.
This is a very rambling piece of fic, with Infected that keep their minds and almost no punctuation. It features a slew of original characters and little coherency.
Sample, including the lack of a period: "wow Rex time has been awful you are small you have gray skin crimson eyes you wear all black but I must admit you look buffer" Dave said as he blew some smoke in Rex's face

"Watching Over Her" by SpontaneousCombustion00. It is located at <a href="http://www.fanfiction.net/s/5413303/1/WatchingOverHer">http://www.fanfiction.net/s/5413303/1/WatchingOver_Her. Rated M.
This is a Zoey/Hunter fic, which features Francis decapitating a zombie with a riot gun while simultaneously pointing a pistol at a Smoker, Zoey not only failing to shoot a Hunter but also allowing it to molest her, and said Hunter being able to talk and remember its name. The Hunter also has eyes which change color.
Sample: "That was a pretty damn good kiss, considering he's an Infected. Zoey thought."