We're running several Left4Dead servers on our dedicated machines located in our Amsterdam datacentre.
The easiest way to connect to our servers, is to join our Steam Community Group. You will then see a list of all our servers in your main menu and can directly join them. We've got servers which are reserved for members of our group, so you will always find a server to play on.
Note: Until Valve releases the next patch, joining through the community group will not allow you to get into a lobby before the game. Therefore you need to adjust the map and difficulty by votes through the in-game menu after you have connected.

Alternatively, you can restrict your lobby server search to only find servers hosted by SpecialAttack. You can do this by setting the CVAR sv_search_key specialattack. You have to enter this command into your console everytime before you start a lobby. If always want to restrict your search results to our servers, you can set this variable through an autoexec.cfg config file or through the launch parameters of Left4Dead. Read more in our forums.