The following list of MIDI devices are USB class-compliant for XP/Vista and 
Mac. (Most interestingly are from m-audio - inexpensive, light weight and 
remarkably well constructed.) On their websites, unfortunately, there is no 
info regarding Linux.

I'd appreciate anyone telling me which of these devices will work with the 
OLPC (XO platform).

m-audio X-session (*not* pro) - 16 pots, 1 slider, compact - probably best 
for my needs
  UC-16 (unfortunately discontinued, but above unit is better anyway)
  UC-33(e) - probably 2nd best for my needs
Novation ReMote Zero SL (expensive; heavier)

Keyboards (compact)
Edirol PCR-30(M) - big, exposed, but all the controls and buttons needed
E-mu Xboard 25 - the only 25 key keyboard with 16 good pots
Korg MicroKontrol - lots of stuff, but pots (8) fairly non-functional (are 
really endless controllers)
m-audio O2 - very compact, keys not exposed; probably best keyboard for my 
needs (8 pots, 1 slider only)
m-audio KeyRig 25 (seemingly identical to the O2)
m-audio Oxygen 49
Novation ReMOTE 25 LE

I'm looking forward to any and all info from you Linux/OLPC folk.

Art Hunkins