my knowledge of living composers extends to john williams, so I have to say him.
But of course, besides the above, he did do a great job w/ starwars/jurrasic park and indiana jones...and probably more, idk about those though
actually now that i get to thinking (a rare happening), quite a few of the songs we play in band are written by living composers, but i can't think of any, except for greg hillis, who wrote "Quest for the Undaunted Knight" which is a great song. But I don't know any of his other songs
then on teh other had there is the finnish legend: kristian setala (aka nerd) whose fugato is a true work of art...
now that i've rambled far past my due, please feel free to add your comments