Hello everyone, I have had to be away from this board for a few days. Glad to see all the posts here! First, I agree with Brownsfan on Britten, though I don't think he is underrated by musicians, anyway.
John Adams - he is most certainly a minimalist composer, and I would agree with Frogman that he is more talented than most. He is certainly more "accessible" than most.
I definitely agree with all of Frogman's nominations, by the way.
And last, I cannot help but comment that Stravinsky has to be considered one of the ten greatest composers ever. He and Bartok both are in there based on sheer compositional craft alone. Let me make another visual art analogy - Stravinsky is the Picasso of music - he could do anything in any style. He is perhaps the only composer other than Mozart who was successful in all genres, too.