This site at Hyde Park Books http://paperbarn.www1.50megs.com/BestSellers/BSLC.htm
has lists of bestsellers from 1900-2002. Especially worth noting for 1900-1910:
Edith Wharton, The House of Mirth was a bestseller in 1905 AND 1906.
Owen Wister's The Virginian and Frank Norris's The Pit shared the honors in 1903 but lest we get too exalted an idea of the audience's taste, Alice Hegan Rice had two books on the list that year: Mrs. Wiggs of the Cabbage Patch and Lovely Mary. More alarmingly, Thomas Dixon (The Clansman) makes a few appearances in this decade, too.