For my part, I can't resist chipping in a mini-eulogy to my favourite composer of all time, Anton Bruckner.
(Much as I love so many of the composers mentioned in this thread, including Rachmaninoff, whose Piano Concerto 2 I have playing as I write this...)
Bruckner's work has really added to my life perhaps almost as much as Ayn Rand's.
All of his symphonies, for me, express emotions of glory, grandeur, awe and exultation. They all contain adagios which express a kind of sad wandering and yearning, but which gradually and inexorably build up and transform into crashing waves of ecstasy and resolution. They all contain scherzos bordered by the relentless energy of 19th century industrialisation, contrasted with inner islands of carefree melody. They always culminate in a massive monumental coda, always ending in a blazing major key, in an atmosphere of celebration and joy.
In every moment of the music, there seems to be something greater being expressed. There is a pervasive "largeness", a sense of a greater unity that can only be appreciated after many listenings, when the music has finally surrendered all of its secrets, and all that's left is to marvel at a lifetime of driven, dedicated handiwork. The last 5 symphonies especially exhibit a cyclic, integrated design, in which elements of every part of the symphony interact throughout the work, and are finally brought together in the finale. The coda of the 8th Symphony does this in a particularly impressive and moving way.
The guy spent his whole life studying and writing music. Clearly he had a passion for the work, and wasn't just trying to be popular or rich. He also spent a significant portion of his life in the Sankt Florian cathedral, an immense, beautifully ornamented structure, one which must have given him inspiration every day. He surely had traits Rand (and I) would disapprove of, particularly belief in God and a bit of an obsession for teenage girls.
That said, I think the idea he was humble or self-doubting is a complete myth. The many alterations he made to his symphonies, rather than humility, seem to evidence a passion and love for the craft and a desire to constantly improve and strive toward perfection. They also offer a fascinating and enjoyable experience in their own right. How many other composers can give you glimpse into two or even three slightly alternative visions of how a single work might have been realised? I find it enriching to see the master reveal some of his process, not just the end result.
I must also add a word of praise for a female composer who I think doesn't get enough attention: Lili Boulanger. The 'Old Buddhist Prayer' in particular strikes me as most exultant and uplifting. Obviously the reference to 'Gods' is a bit suss. But I do love lyrics like: "Let all those beings which exist -- without enemies, without obstacles, overcoming their grief and attaining happiness, be able to move freely, each in the path destined for them". That's the kind of feeling I like to have in my head when I wake up in the morning.
I guess what I get most from both composers is the sense of a world that is large, awe inspiring and full of endless potential.