I finished reading Brokeback Mountain by Annie Proulx (famous for The Shipping News). It was truely amazing. SO I read it again, and the second time things became even clearer, and I was moved even more. The characters of Ennis and Jack were developed in such way that, part of it is what the author describes, another part of it is based on your opinion.
You can really feel the isolation of the cold Wyoming, the prejudice against homosexuals, the unrealised love between the cowboys... Some parts of the book will make you smile with tears, some of the book will make you feel anger, and the ending will break your heart, but at the same time treasure what they have together.
I strongly recommend reading this book. It's rather short, (something like 65 pages), so it won't take you very long. Also watch the trailer for the movie before you read the book - it will make some of the scenes in the book more visual. You can view the trailer of the Apple.com website.
I cannot wait for the movie to come out!! Hope this helped.