When Brian informs his assistant that he's going to Spain (he's actually getting surgery for testicular cancer he says, "Flight 18. Barcelona and Madrid." This is taken verbatim from the lyric to the song "Barcelona" in Stephen Sondheim's "Company" as an homage.
Brian sits down with Gus, who is watching James Dean on television. What they are watching isn't a movie, but rather Dean, dressed as his character from the then-upcoming film 'Giant (1956)', being interviewed by Gig Young as a public service announcement on the dangers of speeding on the highway.