Just saw it for the 3rd time in IMAX 3D, and man, it keeps getting better each time! This time I was paying attention to which scenes were in full IMAX (i.e., taking advantage of the whole screen), and this is what I recall:

Sam on Recognizer, being taken to arena
Disc war
Lightcycle battle
Solar sailer
Rectifier setting sail
Clu's speech to army
Lightjet battle
Final confrontation (I think)

Any scene I missed?