Here is a nifty little site that gives you the bestselling books of each year of the entire 20th Century. It is interesting to see what you've read, what you might like to read (if you could find a copy), and how fickle is popular opinion. I took the first three decades from the list and found those books I've read at some time or another. Here they are -- with the titles in bold print that I would recommend as quality literature.
From 1900: #5. Eben Holden by Irving Bacheller (also #5 in 1901) and #8. Richard Carvel by Winston Churchill. (Both of these I just read in the last year or so.)
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, 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 byEugene 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.
Check out the lists for yourself. If you're interested in books (and why would you be at The Book Den if you weren't?), you'll find it fun.