First, I just played Nebjosa Jovan Zivkovic's "Ultimatum II" (for two 5-oct). It's adavanced and REALLY fun to play. I highly reccomend it. There's a recording of Zivkovic and Benjamin Toth playing it on NJZ's disk "In the Castle of the Mad King". Secondly, "Diptych No.3" for two marimbas by Gordon Stout is also very cool. A recording of that is on Michael Burrit's "Perpetual" Finally, "Conversation in the Forrest" by Keiko Abe. Perhaps my favorite marimba duet of all. On the top of my list for sure.