Season 3

Season 3 deals with the two boys trying to hunt down and kill the demons that were released from hell's gate in Season 2. We start to see Sam changing into a character that seems to have less remorse for his victims. He is starting to change, just like the "yellow eyed demon" said he would. Now that Sam has refused his role as leader of the demons, a new demon is chosen, Lilith. She has possessed a little girl and is attempting to raise her master, Lucifer. Also, the end of the season marks the one year mark of Dean's deal with the crossroad demon. There are hellhounds sent after him and they eventually catch up and kill him. Season 3's last seen is Dean in hell.

Dean in Hell - http://1.bp.blogspot.com/_cr1FMICemSA/SfdNvWsy9oI/AAAAAAAAA7s/Y4i9lMiSWM0/s400/wmplayer+2008-05-16+16-24-27-15.jpg

Now, Season 4