I am not a stoner, and I have never seen any of the movies, so I am going off of the comments on IMDB, YouTube and Amazon for this, but I think that a fantastic selection for the podcast would be the movie Evil Bong.
It's about three stoners who get a possessed bong from the back of a magazine that... I don't even know. I can't tell, the trailer is terrible, here, try to decypher it yourself: http://youtu.be/a6hT0qFnucM
The second movie is called Evil Bong 2: King Bong and the third is Evil Bong 3: Wrath of Bong.
I figure these would make a good movie to watch close to the end of April. And since there are three of them you could have the same guest on each time. Now, if only there were a comedian that loves both Pot and Movies. Hmm... If only there were someone who dug both marijuana and the cinema. Maybe if there were some comic who had a weekly podcast with a nearly impossible to describe movie based game that the guests constantly mess up while playing.
What I'm saying is make it up to Doug Benson and have him watch these too. Though they seem pretty terrible, so it might be more of an additional punishment in addition to the Twilight films.