Thanks to N8 for these:
Best Sound Editing: Sound Effects, Foley, Music, Dialogue and ADR Animation in a Feature Film
Wall-E
Best Sound Editing: Sound Effects, Foley, Dialogue and ADR in a Foreign Feature Film
Slumdog Millionaire
Best Sound Editing: Music in a Feature Film
The Dark Knight
Best Sound Editing: Music in a Musical Feature Film
Mamma Mia!
Best Sound Editing: Dialogue and ADR in a Feature Film <–important award
The Curious Case of Benjamin Button
Best Sound Editing: Sound Effects and Foley in a Feature Film <–super important award
The Dark Knight
A little history. Last year, Bourne Ultimatum won these last two and then went on to win the Oscar.   Letters from Iwo Jima won Sound Effects and Foley and then went on to win the Oscar for Sound Effects Editing.
Thus, if you go by the CAS and by the MPSE, you’d have Slumdog for mixing and Dark Knight for editing.