a few medtner sonatas, particularly the night wind sonata come to mind. lets face it, the man was a genius and the greatest composer of his time (i quote rachmaninoff). also beethoven's op 109 sonata is one of the best ive heard of that era. the berg op 1 sonata is one of the best "pre-contemporary" sonatas. from the last 40 years, it is impossible to make one choice, but i will nominate vine's two published sonatas and kapustin's 2nd sonata. there are just too many from the romantic era that i could name, but the night wind sonata by medtner and alkan's grande sonata are way up there.