I just got back from seeing the SUNY Stony Brook Percussion Ensemble perform Reich's Music for 18 Musicians. It is such a great piece. Reich is the original innovator, probably the most important composer of drum music well, I would say of the 20th century but that would make it like ever. I've heard his ensemble on several occasions and it has always been mind -blowing.
In Musician for 18 Musicians the two central percussionist, first on marimba and then on xylophone, and then the marimbas return, keep an ostinato where one guy is holding down as 8th note pulse and the other plays the 16th upbeats to that.