Shaolin and Wu Tang (1981)
This is the 1981 martial arts film that Wu-Tang Clan took their name and part of their concept from. The film features two warring martial arts clans.
Wu: The Story of the Wu-Tang Clan (2007)
This is a middle-of-the-road BET documentary that will still be great fun for fans.
"Kung Fu Movies Which Influenced the Wu-Tang Clan's Music"
An extensive list brought to you by amazon.com; it may be based on non-expert knowledge, but it looks like a pretty fun bunch of movies.