Here is a nifty site that gives you the bestselling books of each year in the entire 20th Century. I found it intriguing to see what books were popular with earlier generations of American readers and how those choices related to books that I myself have read. You might find it of interest too.
And in addition to comparing what they read with what you've read, you might also find a few titles for future reading. After all, services like Project Gutenberg are making available (for downloading onto a Kindle and other e-readers) a lot of books that have long been out of print. That's very cool. For as a historian (as well as an aficionado of wholesome literature), I find it exciting to be able to read books that informed, entertained and even inspired those who went before me.
Anyhow, here's one result of my engagement with this 20th Century book list. I scanned just the first three decades looking for books that I had read at some time or another. I print them below. Not all of them were gems, of course. So please note that only the titles I put in bold print are books that I would heartily recommend to others.
From 1900: #5 -- Eben Holden by Irving Bacheller (also #5 in 1901) and #8 -- Richard Carvel by Winston Churchill. (This, by the way, is the American author Winston Churchill, not the other one.)
1902: #1 -- The Virginian by Owen Wister (also #5 in 1903) and #7 -- The Hound of the Baskervilles by Arthur Conan Doyle.
1905: #4 -- The Clansman by Thomas Dixon Jr.
1906: #6 -- The Jungle by Upton Sinclair.
1913: #8 -- Pollyanna by Eleanor H. Porter (also #2 in 1914).
1914: #3 -- The Desert of Wheat by Zane Grey. Also in the Non-Fiction category (It looks like they started keeping track of this genre in 1912.), I've read #1 -- The Education of Henry Adams by Henry Adams.
1920 Non-Fiction: #3 -- Roosevelt's Letters to His Children, Joseph B. Bishop, editor.
1921 Non-Fiction: #1 -- The Outline of History by H. G. Wells (also #1 in 1922 and #5 in 1923).
1925 Non-Fiction: #3 -- When We Were Very Young by A. A. Milne and #4 -- The Man Nobody Knows by Bruce Barton (also #1 in 1926).
1926 Non-Fiction: (besides Barton's) 8 -- The Story of Philosophy by Will Durant (also #1 in 1927).
1927 Non-Fiction: (besides Durant's) #3 -- Revolt in the Desert by T. E. Lawrence
1928: #1 -- The Bridge of San Luis Rey by Thornton Wilder and #4 -- The Greene Murder Case by S. S. Van Dine. Also, wrongly put in the Non-Fiction category (it is a play) is #5 -- Strange Interlude by Eugene O'Neill
1929: # 1 -- All Quiet on the Western Front by Erich Maria Remarque and #4 -- The Bishop Murder Case by S. S. Van Dine. Also, at #8 in the Non-Fiction category (again, wrongly put) is the narrative poem, John Brown's Body by Stephen Vincent Benét.
Again, here is the list. Go begin your own adventures.