I also see Luke as sort of a pawn in the Master/Apprentice feud between the two; Vader was thinking he could turn Luke into his apprentice and overthrow the Emperor, becoming Sith Master and Emperor himself; Palpatine felt, perhaps, that Vader's injuries made him a bit disappointing in the end, and needed a fresh apprentice without Vader's weakness. Of course they didn't really say this out loud to each other, although they both let Luke now-Vader in ESB, The Emperor in ROTJ.
Vader also offered Padme a similar deal in ROTS although she didn't seem to have the force so I'm guessing it was more like he would have her around as a Queen and she'd be helpful in dealing with the politics (probably not Anakin's forte).
Both Vader and Palpatine told each other openly that he would be an ally, I guess a "dark jedi" like in the old EU, or something like the Inquisitors in the new. But both had ambitions beyond that.
Marvel's Vader comics (both of them) I think have done a good job at showing the quiet struggle for power between the two.