BluRay player for rMBP
I have a Sony bluray burner I got on Amazon for 70 bucks (Samsung SE-506CB/RSBD). I know you said you didn't need a burner but it's a quality drive.
That said, playing blurays on a Mac, or any computer has been a fairly poor experience for me. Maybe others will vary but even with what seemed to be quality Bluray playing software (Mac Bluray player) it's very hit and miss.
What software were you planning to use to play your blurays? I'm curious to hear what everyone else is using too.