For those of you who want to skip the intro videos and load right into the main menu, right click on Left 4 Dead 2 in Steam client to open the game's properties window. In the General tab, click the Set Launch Options button to open the Launch Options window. Type in this text box, -novid and click OK. Now when you launch the game from Steam, it will skip the intro videos and go straight to the main menu, saving you a few clicks as well as a few seconds.
If you want to disable all L4D2 menu music, you can delete the folder /steam/steamapps/common/left 4 dead 2/left4dead2/sound/music/l4d2/, but when the game updates itself it might also redownload these files. If you verify the game cache, it will definitely redownload these files. If you want an easier and more permanent solution, download this .vpk I made that overwrites the lobby music with blank files. Because it's in a .vpk, it won't be overwritten, and if you wish to disable or enable it, it's easier to do.
I'd much prefer the menu music to play once, then fade out and not loop again (like it does in L4D1). I know how to do it (I think) but I haven't found file that controls that yet. I'll keep on it, though.