Eureka! I posted about the prosody of the phrase "yeah right" some time ago here. In particular, I claimed there are 3 three interpretations of the phrase, but I don't have one of them in my dialect (Northern California), namely what I called "back-channel (sentiment agreement)" which is roughly equivalent to ‘mm-hmm’. However, I had no sound files. Now I've found a near perfect example of this mystery prosody in the trailer for Juno, about 36 seconds in (here).
You can also read my most excellent review of Juno here.