Finally a decent "official" alternative to the openserverbrowser console command in l4d:
Left 4 Dead has been updated to include a lobby browser. The lobby browser (under Play Online) will show you a list of optimal games available for you to join. The browser pares down the thousands of lobbies and games currently being played to show you the best list of games available to you. This list includes official and add-on campaigns, including add-on campaigns you have not yet installed, making it a great way to discover them. You can filter by difficulty, official and/or add-on campaigns and by lobbies and/or games in progress. Find out more on the L4D blog.