Wizards of the Coast has discontinued a number of the AD&D campaign settings, including Ravenloft, effective with AD&D 3rd Edition. Some Ravenloft characters and concepts will be incorporated into the main game.
Gaming materials are becoming rare, however, as long as significant interest remains the Ravenloft campaign setting it will be supported in some capacity. Until 2003 it was supported through the "official" Ravenloft site, www.kargatane.com, but that site has since ceased updating.
A successful Ravenloft campaign is different from your typical AD&D slash and hack. It focusses more on character development and role-playing in the gothic setting of Ravenloft. Ravenloft rekindled my interest in AD&D, allowing me to explore the themes of corruption, betrayal and redemption in an RPG setting.
Among the tools in the Ravenloft DM's kit is good mood music. I recommend the soundtracks to Conan the Barbarian, Sleepy Hollow and Bram Stoker's Dracula , and Midnight Syndicate's "original soundtrack" CDs.
2016 update! A Dungeons & Dragons Sourcebook for 5e (fifth edition), Curse of Strahd was released in March 2016. Further updates once I obtain a copy...