These are the top 106 books most often marked as "unread" by LibraryThing's users (as of a little while ago). As usual, bold what you have read, italicize what you started but couldn't finish, and strike through what you couldn't stand. The numbers after each one are the number of LT users who used the tag of that book.
In some cases, I think I have read it, but I can't remember anything about it, so I may not have. I've left those unmarked.
The Aeneid (45)
The Amazing Adventures of Kavalier and Clay (52)
American Gods (68)
Anansi Boys (58)
Angela's Ashes : A Memoir (51)
Angels & Demons (56)
Anna Karenina (132)
Atlas Shrugged (67)
Beloved (49)
Brave New World (61)
The Blind Assassin (73)
The Brothers Karamazov (80)
Catch-22 (117)
A Clockwork Orange (59)
Cloud Atlas (47)
Collapse : How Societies Choose to Fail Or Succeed (47)
A Confederacy of Dunces (50)
Crime and Punishment (121)
Cryptonomicon (50)
The Canterbury Tales (64)
The Catcher in the Rye (46)
The Confusion (46)
The Corrections (53)
The Count of Monte Cristo (59)
The Curious Incident of the Dog in the Night-Time (52)
David Copperfield (44)
Don Quixote (91)
Dracula (59)
Dubliners (50)
Dune (51)
Eats, Shoots & Leaves: the Zero Tolerance Approach to Punctuation (48)
Emma (73)
Foucault's Pendulum (61)
The Fountainhead (61)
Frankenstein (59)
Freakonomics : A Rogue Economist Explores the Hidden Side of Everything (45)
Gravity's Rainbow (44)
The God of Small Things (51)
The Grapes of Wrath (57)
Great Expectations (70)
Gulliver's Travels (53)
Guns, Germs, and Steel: the Fates of Human Societies (79)
A Heartbreaking Work of Staggering Genius (67)
The Historian : A Novel (63)
The Hobbit (44)
The Hunchback of Notre Dame (45)
The Iliad (73)
In Cold Blood : A True Account of A Multiple Murder and Its Consequences (44)
The Inferno (56)
Jane Eyre (80)
Jonathan Strange & Mr Norrell (149)
The Kite Runner (71)
Les Misérables (53)
Life of Pi : A Novel (94)
Lolita (46)
Love in the Time of Cholera (62)
Madame Bovary (83)
Mansfield Park (55)
Memoirs of A Geisha (66)
Middlemarch (61)
Middlesex (66)
The Mists of Avalon (47)
Moby Dick (86)
Mrs. Dalloway (70)
The Name of the Rose (91)
Neverwhere (50)
1984 (57)
Northanger Abbey (46)
The Odyssey (83)
Oliver Twist (54)
On the Road (46)
The Once and Future King (57)
One Flew Over the Cuckoo's Nest (54)
One Hundred Years of Solitude (115)
Oryx and Crake : A Novel (47)
A People's History of the United States : 1492-Present (51)
Persuasion (46)
The Picture of Dorian Gray (55)
The Poisonwood Bible : A Novel (57)
A Portrait of the Artist As A Young Man (63)
Pride and Prejudice (83)
The Prince (51)
Quicksilver (66)
Reading Lolita in Tehran : A Memoir in Books (66)
The Satanic Verses (55)
The Scarlet Letter (48)
Sense and Sensibility (55)
A Short History of Nearly Everything (50)
The Silmarillion (104)
Slaughterhouse-Five (49)
The Sound and the Fury (51)
A Tale of Two Cities (80)
Tess of the D'urbervilles (54)
The Three Musketeers (44)
The Time Traveler's Wife (73)
To the Lighthouse (54)
Treasure Island (44)
Ulysses (84)
The Unbearable Lightness of Being (49)
Vanity Fair (74)
War and Peace (78)
Watership Down (44)
White Teeth (44)
Wicked : the Life and Times of the Wicked Witch of the West (65)
Wuthering Heights (110)
Zen and the Art of Motorcycle Maintenance : An Inquiry Into Values (45)
In some cases, I think I have read it, but I can't remember anything about it, so I may not have. I've left those unmarked.
The Aeneid (45)
The Amazing Adventures of Kavalier and Clay (52)
American Gods (68)
Anansi Boys (58)
Angela's Ashes : A Memoir (51)
Angels & Demons (56)
Anna Karenina (132)
Atlas Shrugged (67)
Beloved (49)
The Blind Assassin (73)
The Brothers Karamazov (80)
Catch-22 (117)
A Clockwork Orange (59)
Cloud Atlas (47)
Collapse : How Societies Choose to Fail Or Succeed (47)
A Confederacy of Dunces (50)
Crime and Punishment (121)
Cryptonomicon (50)
The Canterbury Tales (64)
The Catcher in the Rye (46)
The Confusion (46)
The Corrections (53)
The Count of Monte Cristo (59)
The Curious Incident of the Dog in the Night-Time (52)
David Copperfield (44)
Don Quixote (91)
Dracula (59)
Dubliners (50)
Dune (51)
Eats, Shoots & Leaves: the Zero Tolerance Approach to Punctuation (48)
Emma (73)
Foucault's Pendulum (61)
The Fountainhead (61)
Frankenstein (59)
Freakonomics : A Rogue Economist Explores the Hidden Side of Everything (45)
Gravity's Rainbow (44)
The God of Small Things (51)
The Grapes of Wrath (57)
Great Expectations (70)
Gulliver's Travels (53)
Guns, Germs, and Steel: the Fates of Human Societies (79)
A Heartbreaking Work of Staggering Genius (67)
The Historian : A Novel (63)
The Hobbit (44)
The Hunchback of Notre Dame (45)
The Iliad (73)
In Cold Blood : A True Account of A Multiple Murder and Its Consequences (44)
The Inferno (56)
Jane Eyre (80)
The Kite Runner (71)
Les Misérables (53)
Life of Pi : A Novel (94)
Lolita (46)
Love in the Time of Cholera (62)
Madame Bovary (83)
Mansfield Park (55)
Memoirs of A Geisha (66)
Middlemarch (61)
Middlesex (66)
The Mists of Avalon (47)
Moby Dick (86)
Mrs. Dalloway (70)
The Name of the Rose (91)
Neverwhere (50)
Northanger Abbey (46)
The Odyssey (83)
Oliver Twist (54)
On the Road (46)
The Once and Future King (57)
One Flew Over the Cuckoo's Nest (54)
One Hundred Years of Solitude (115)
Oryx and Crake : A Novel (47)
A People's History of the United States : 1492-Present (51)
Persuasion (46)
The Picture of Dorian Gray (55)
The Poisonwood Bible : A Novel (57)
A Portrait of the Artist As A Young Man (63)
Pride and Prejudice (83)
The Prince (51)
Quicksilver (66)
Reading Lolita in Tehran : A Memoir in Books (66)
The Satanic Verses (55)
Sense and Sensibility (55)
A Short History of Nearly Everything (50)
The Silmarillion (104)
Slaughterhouse-Five (49)
The Sound and the Fury (51)
A Tale of Two Cities (80)
Tess of the D'urbervilles (54)
The Three Musketeers (44)
The Time Traveler's Wife (73)
To the Lighthouse (54)
Treasure Island (44)
Ulysses (84)
The Unbearable Lightness of Being (49)
Vanity Fair (74)
War and Peace (78)
Watership Down (44)
White Teeth (44)
Wicked : the Life and Times of the Wicked Witch of the West (65)
Wuthering Heights (110)
Zen and the Art of Motorcycle Maintenance : An Inquiry Into Values (45)