In one of the conversations between Ash, Brock and Claptrap, they will talk about the planet Pandora from the Borderlands series. During the conversation they'll say:

Brock: Yeah, about that. I always heard that Pandora was some sort of lush jungle paradise.
Ash: Yeah, me too. What happened, did you guys run out of the, what was it - Cantgetium?
Brock: Nah, I think it was called "Macguffinite."
Claptrap: Ha. Ha. Very funny. Look, MY Pandora was first, got it?
Ash: All right, all right. Jeez. One question, though.
Claptrap: What?
Ash: What's James Cameron really like?
Claptrap: @#$% you.

This is a reference to the 2009 film Avatar by James Cameron which also features a planet named Pandora and contains the valuable mineral "unobtanium".
Contributed by KnowledgeBase