So as I mentioned before, this being the official site for my Custom L4D2 Server, I wanted to lend a hand to all the people that start a L4D2 server for the first time.
The process can be very easy depending on the GameServer host you choose... I have mine linked at the bottom, but I would also recommend http://www.techwebhosting.com/game.php. The reason I recommend them is that they are very low price, starting at 99 cents per slot. Now depending on whether you play Campaign mode or Versus, this company allows you to choose a 4 man server which is all you need for everything except versus. Me personally, I don't like versus... so I choose 4 slot Public which is 4.96, now I come across a promo code for 30% off for life of server... l4dforums. This is very cheap for this service and they even upload maps and install mods for you so that you don't have to, will setup your entire server.
I have also linked a Guide to creating and setting up a server from the Steam Forums here. The only other thing to know is that it is hard to change weapon setting such as damage dealt and ammo in each gun in L4D2. Sourcemod.net, is the site to get plugins and admin mods that will be very useful on your server.
If you have any questions on how to set one up, please let me know!