Moon, is probably my favorite movie of 2009.  It's definitely in the top 3.  It's a  Sci-fi movie, with many similarities to 2001: A Space Odyssey.  If you like that type of movie then I suggest you look no further into learning about the plot.  Just go into it with as little knowledge as possible to get the best of the movie.  I havn't included the wikipedia link this time because it gives away the entire movie.  So only check out IMDB, no spoilers there.

In case you are wondering, my other favorite movies of 2009 will be posted soon!

More at IMDB