Well tell me, what is wrong with Haydn, Mozart, and Beethoven?
Look into Clementi, not his popular pieces that are taught to young students, those pieces don't even begin to do him justice. He wrote some very beautiful sonatas.
Are you familiar with Haydn's F minor Variations? This one of the most beautiful and heartfelt pieces in the literature as far as I'm concerned. Also check out Mozart's C minor Fantasy, K. 475. You don't hear these two pieces nearly as often as their sonatas.
C.P.E. Bach would be a nice alternative, check out his sonatas and fantasias.