Dean discourages Sam from returning to Plucky's, saying, "The one guy who was gonna rat, he got Bruced." He is referring to the mechanical shark Bruce from the horror classic Jaws (1975).
The theme music/song heard while Sam is at Plucky Pennywhistle's is the same music used in the Season 7 Gag Reel.
When Cliff confesses about the meth lab and Dean says he doesn't care if he "Broke Bad", he is referring to the popular AMC series Breaking Bad (2008).
Before Sam shoots one of the clowns he says "if it bleeds you can kill it." A reference to the movie Predator (1987).
When Sam suggests that something on a horse killed Billy's dad, Dean says, "Close but no Seabiscuit." He is referring to the thoroughbred racehorse, Seabiscuit, an unlikely champion and symbol of hope in the Great Depression.