The Whattorent.com site is kind of like a collaborative filter, except it recommends movies you should rent based around a one-time personality quiz and a simple on the spot ‘mood’ filter. Register, answer your profile questions and the next time you fancy watching something but don’t know what, log on.
Tell it what kind of mood you’re in and it will suggest something. It’s quite cool I think, since the first two choices it gave me were pretty close (the first one I’d seen and liked and the second starred Bill Murray who I usually like). Definitely worth a peruse if you’re stuck of a rainy evening.