L4D2 Sound Mod Creator
The Sound Mod Creator is a program made by "LUKeM a.k.a Neil - 119" over at the l4dmaps community. Its purpose is to simplify the creation of basic L4D2 sound mods. You can download it here.
How It Works
The tool scans for available Source games and enumerates a list of all available sounds for each game. Then, it allows the user to browse the sounds, filter by name, replace existing sounds with custom MP3s/WAVs/OGGs etc. Moreover, it handles all file type/length/bitrate conversions internally through ffmpeg. Lastly, the program can package VPKs for sharing sound mods with friends.