It may be a little late, and this is not on-line, but I have a copy of Joel Whitburn's Pop Memories 1890-1954, which is a compilation of the hit records from every year--granted, he doesn't list the most popular sheet music, but he has the top ten by decade, as well as the top one hundred hits--here's a sample--from 1893, the number one records included: 'The Bowery(sung by Dan Quinn), Oh, Promise Me(George Gaskin), After The Ball(George Gaskin), Daisy Bell (Dan Quinn), The Fatal Wedding (George J. Gaskin)--Yankee Doodle Dandy hit the charts the next year, as did Dem Golden Slippers, and The Sidewalks of New York topped the charts in 1895--

The Levy site is a good place to look if you konw what you want, but it doesn't give you any idea of how popular anything was, and especially no idea of whether people will like it now--