The Wicker Man is a fabulous movie, which was not nearly well known enough here in America (until the wretched remake, that is*).
In this well-written gem, an upright policeman goes to a Scottish island looking for a missing girl about whom he received an anonymous letter. The people of the island are not particularly helpful with his search. During his investigation he discovers all sorts of indecent goings-on--sexual, pagan rituals that make the good church-going policeman quite uneasy and rightly so.
It's an incredibly well-written story, with a simple, but interesting plot with a truly shocking ending. Set in contemporary times, it sustains an uneasy atmosphere and includes a number of sometimes funny, but often unsettling folk musical numbers. It also includes a fabulous performance by Christopher Lee as Lord Summerisle, pagan leader with quite the head of hair. There's lots of excellent quotes by Lord Summerisle such as "Do sit down, Sergeant. Shocks are so much better absorbed with the knees bent." It's a terribly quotable script. Despite all of the quirky townspeople, odd musical numbers and showy performance by Lee, Edward Woodward keeps the film from turning campy with his excellent, restrained performance.
This film also has quite an interesting backstory. This website explains the backstory well, and outlines the various versions. Try to find the version with 97 minutes (at least) of footage. The hacked-up American version (at 88 minutes or so) is too choppy to establish the suspenseful tone.
* Watch out for the 2006 remake starring Nicholas Cage that completely destroys the original story and inserts a matriarchal society of evil. The movie, made by the always charming and not at all misogynist Neil LaBute, includes a truly bewildering number of scenes where Cage's character beats up women and provides only unintentional humor, mostly due to Cage's wild overacting. Check out any video on YouTube that mentions this movie and bees for a sneak peek.