MovieLens
Movielens is a great site by the University of Minnesota that was recommended to me by Markos. It works like this: You rate movies you've seen and it makes recommendations based on your profile. The more you rate, the better the recommendations are. From the little time I've spent rating movies there, its recommendations are great: it clusters people based on their ratings and as such it starts recommending 'good' movies almost immediately. Within the first 5 minutes of my registration it started recommending movies I'd seen and that I've liked. This also accelelerates the learning process as you can rate the movies you've already seen much faster than a chonological, genre-based or other listing might allow. In about 40 minutes I managed about 250 movies I'd seen and liked, several times faster than what's possible with IMdB.
If anything, MovieLens represents what IMdB sorely needs: a good recommendation service.