Dataset from Netflix's competition to improve their recommendation algorithm. See also http://academictorrents.com/details/9b13183dc4d60676b773c9e2cd6de5e5542cee9a
Netflix held the Netflix Prize open competition for the best algorithm to predict user ratings for films. The grand prize was $1,000,000 and was won by BellKor's Pragmatic Chaos team. This is the data