i kinda have a gut-feeling tht ruby did something..don't know for sure

well, not sam..only the situation..we can't blame sam for dying.

John, for raising Dean to think that Sam was more important than him. If John hadn't placed so much emphasis on protecting Sam, then maybe Dean wouldn't have felt so horribly guilty about Sam's death and wouldn't have sacrificed himself.

well this is hard because i agree with fanfly in a way...i think john selling his soul for dean made him think even less of himself then when sam died he felt that it was his job to protect him even in death.....remember what he said to bobby in AHBLP2 he said that this way his life could mean something....so in a way it's both john and sam's fault...but on sam's part i think it's more the situation like lucysmileyface

No one should blame sam it was deans chioce and lilith took him to hell so dont blame sammie !!

I too think it was mostly John's fault.
First all the protect-Sam-with-your-life thing, then knowing that your father sold his soul to save you and finally Sam's death on top of all that was Dean's limit. I think he just couldn't take it anymore and commited a 'suicide'. Yes, I think selling your soul is commiting a suicide.

I picked Sam, but not as the CAUSE, more so the reason. I love Dean and was horrified when he died, but nobody twisted his arm to make that deal. I don't think it was guilt so much as Dean thinking he could not go on without Sam; his biggest fear has always been ending up alone. He got a crap deal, but HE made the choice - simply because he loves his brother so much and he was willing to sacrifice himself. Sam was equally willing to do the same thing for Dean, but, "no demon would deal." *Sigh* Those brothers! God how we love them!