For a great discussion/dissection of the seesaw relationship of fear and desire, I commend you to Mike's post of yesterday.
As for me, I'm taking the easy way out and turned to the internet to dig up lists of movies and books that are touted at excelling at exploring these two very primal emotions.
No surprise to me, when I perused The Taste of Cinema's list of "15 Great Horror Movies that Tap into Existential Fear" that I have only seen two of the ones listed: The Birds and Alien... and if I'd known how the Alien was going to unfold, I probably would have avoided it!
As for "desire"... it isn't always about sex, is it? Well, you'd think so if you try to uncover lists about movies dealing with this emotion. There is "The 20 Best Movies about Repressed Sexuality" (ooookay), "15 Great Films that Explore Sadomasochistic Desire," (well now), and the "12 Most Erotic Non-Sex Scenes in Movie History," there's plenty to choose from, and very few which I have seen, so don't ask me for recommendations.
Regarding the last list (most erotic non-sex scenes), someone posted a comment mentioning the Lauren Bacall and Humphrey Bogart scene in To Have and Have Not in which she reminds him "how to whistle," so of course I had to chase it down on YouTube:
And then... I found a movie that combines both emotions (at least in the title):
Fear and Desire, a 1953 American anti-war film that was directed, produced, shot, and edited by Stanley Kubrick.
Having never seen it, I can't comment as to how thoroughly the movie covers fear and desire or whether one is more emphasized than the other, although the fact that Kubrick's movie (! his first feature film !) is paired with one titled The Male Brute might provide a hint.
So what about you? Any suggestions for movies that do a good job wrapping fear and desire in one cinematic package? Let us know!