The innovative TV network Current has a training section on the principles of filmaking. Short videos cover topics in storytelling, gear, shooting, editing and compression. The nicely designed tutorials give tips for making amateur films look more professional.
Amateur film-makers might also enjoy watching some Dogme 95 films for examples of great movies that use natural setting and lighting. Here's a pretty complete list from Wikipedia of movies that adhere to the principles.
Speaking of amateur filmmaking, if you are a 24 fan and enjoyed My Space: The Movie (which has been getting plenty of attention), you might enjoy this guy's home-made film about the theft of his Season 3 box set: