I found this while I was helping Whiskey with the server. I thought it might be useful for everyone to get a look at. Of particular note are the CallVote functions, which can be used to restart the game. To use in game, type 'CallVote' in the console. You'll get a series of options. For instance, to restart the game you'd open the console and type 'Callvote Restartgame'. This would then initiate a vote to restart the game.
You can enable the developer's console in the mouse and keyboard options menu in L4D. You open the dev console by hitting ~ in game.
Here's the link to the complete list, all 121 pages of it.
www.undeadgames.com/links/l4d_cvar_list.pdf
