I think you guys might enjoy this soundpack for Left 4 Dead 2, just updated for "The Sacrifice" DLC, which enhances/replaces over 1,700 sound files for the game, plus 15 high-quality custom textures. It features months of original work by a professional sound designer & is NOT a compilation of other mods.

Download it here:

Bilian's L4D2 Sound & Music Replacement Mod v1.1 addon - Mod DB

There are 7 videos on youtube.com demonstrating gameplay with the mod, here is the latest:
YouTube - Bilian's L4D2 Sound & Music Replacement Mod v1.1 (Updated For "The Sacrifice" DLC).avi
Here are the other 6:
YouTube - Bilian's L4D2 Sound & Music Replacement Mod Plus v1 (Part 1 of 6: INFECTED & ZOMBAT SOUNDS).avi
YouTube - Bilian's L4D2 Sound & Music Replacement Mod Plus v1 (Part 2 of 6: SPECIAL INFECTED).avi
YouTube - Bilian's L4D2 Sound & Music Replacement Mod Plus v1 (Part 3 of 6: STARTING MUSIC & FIREARMS).avi
YouTube - Bilian's L4D2 Sound & Music Replacement Mod Plus v1 (Part 4 of 6: MENU MUSIC).avi
YouTube - Bilian's L4D2 Sound & Music Replacement Mod Plus v1 (Part 5 of 6: JUKEBOX MUSIC).avi
YouTube - Bilian's L4D2 Sound & Music Replacement Mod Plus v1 (Part 6 of 6: CONCERT FINALE).avi