...okay for the last time the song in the Pineapple Express movie trailer is "Paper Planes" by M.I.A.
The song's childrens chorus punctuated by gunshots, fits well with a goofy robbery movie.
On its own the song is an odd. For an artist 's forming a voice against exploitation and violence M.I.A. ends up kids and guns to sell a song/album. Now I'm gonna be honest, I really like her (and her shows are fantastic) but I'm not gonna claim to fully understand the lyrics behind every song ("Galang-a-lang-alang" ?). So it's possible that she's telling the narrative from a third person's perspective. But like, I dunno... That being said who gives a shit, the song (and album) rocks.
What's more important is how awesome Franco and Seth Rogen are. I loved them in the old TV show "Freaks & Geeks" and it's cool to see them back. James of course was the lead slacker and Seth was the sarcastic beer lover who at the conclusion of the first (and only) season ended up dating a girl who was a guy.