Search advice:

• Video downloads: Other than movie trailer and production clips, that is.
• Exploration: Site components that show the visitor what the world characterized by the movie or other product would be like. Something like a faux web site, but smaller-scale, and often built as part of a regular promotional site.
• Social networking: Web-based services for tracking and developing personal relationships: Facebook, Twitter, and the like.
• Simple interactive games: Simple games, usually Flash-based, that are themed around the product being promoted. Maybe a "target practice" game for a war movie or an "escape" game for a spy movie. (Personal note: I usually don't consider these particularly immersive and so am not spending much time on them, but they show up on a lot of sites, so they're worth mentioning.)