1. Parks and Recreation references The West Wing

On the Parks and Recreation episode "Live Ammo," Bradley Whitford guest stars and reunites with former West Wing cast member Rob Lowe. Their characters in The West Wing, Josh Lyman and Sam Seaborn, worked together as senior staff under President Bartlett. Though they're still working in the government in Parks and Recreation, they seem to have been massively demoted to Pawnee. Whitford plays Councilman Pillner and while he's never in the same room at Chris Traeger (Lowe), the writers at Parks don't forget to throw in a little tribute to The West Wing.