Season 2

SEASON 2  Sam and Dean spend most of the season hunting down Azael, the yellow eyed demon that killed both of there parents.  Bobby their adopted father helps out a lot.  Bobby will be showing up whenever the boys need help throughout the series.  Following the journal that John left behind the boys end up at The Roadhouse.  The Roadhouse, a popular place for hunters, is run by Ellen Harvelle an old acquaintance of John's, her daughter Jo and Ash the 'genius'. Like Bobby they help out the Winchesters. Another character that keeps coming back is (spoiler) the Trickster.  Personally I love this guy's sense of humor.  He is crazy and his favorite toys are Sam and Dean.  At the bottom is the Gag Reel from Season 1 

Winchester pranks

Big time Bad Guy Azael

Ash

The boys' adopted father

Trickster

Ellen and Jo Harvelle