Ganked from several.
These are the top 106 books most often marked as "unread" by LibraryThing's users (as of whenever whoever started this meme looked). As usual, bold what you have read, italicise what you started but didn'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 (that is, last time that the algorithm was done).
Jonathan Strange & Mr Norrell (149)
Anna Karenina (132)
Crime and Punishment (121)
Catch-22 (117)
One Hundred Years of Solitude (115)
Wuthering Heights (110)
The Silmarillion (104)
Life of Pi : a novel (94)
The Name of the Rose (91)
Don Quixote (91)
Moby Dick (86)
Ulysses (84)
Madame Bovary (83)
The Odyssey (83)
Pride and Prejudice (83)
Jane Eyre (80)
A Tale of Two Cities (80)
The Brothers Karamazov (80)
Guns, Germs, and Steel: the Fates of Human Societies (79)
War and Peace (78
Vanity Fair (74)
The Time Traveler's Wife
The Iliad (73)
Emma (73
The Blind Assassin (73)
The Kite Runner (71)
Mrs Dalloway (70)
Great Expectations (70)
American Gods (68)
A heartbreaking work of staggering genius (67)
Atlas Shrugged (67)
Reading Lolita in Tehran : A Memoir in Books (66)
Memoirs of a Geisha (66)
Middlesex (66) Wonderful book. Possibly my favorite of the titles on this list.
Quicksilver (66)
Wicked: The Life and Times of the Wicked Witch of the West (65) Maybe hated is too strong. But it is so well loved that I feel like being the lone voice in the wilderness whenever it comes up.
The Canterbury Tales (64)
The Historian : A Novel (63)
A Portrait of the Artist as a Young Man (63) Picked it up for AP English class, read about ten pages, put it down. I have never read anything else by Joyce since.
Love in the Time of Cholera (62)
Brave New World (61)
The Fountainhead (61) I read this in college when I didn't know enough to hate it. If I tried to read it now I'm sure it would get a strikethrough...
Foucault's Pendulum (61)
Middlemarch (61)
Frankenstein (59)
The Count of Monte Cristo (59)
Dracula (59)
A Clockwork Orange (59)
Anansi Boys (58)
The Once and Future King (57)
The Grapes of Wrath (57)
The Poisonwood Bible : A Novel (57)
1984 (57)
Angels & Demons (56)
The Inferno (56)
The Satanic Verses (55)
Sense and Sensibility (55)
The Picture of Dorian Gray (55)
Mansfield Park (55)
One Flew over the Cuckoo's Nest (54)
To the Lighthouse (54)
Tess of the D'Urbervilles (54)
Oliver Twist (54)
Gulliver's Travels (53)
Les Misérables (53)
The Corrections (53)
The Amazing Adventures of Kavalier and Clay (52) I loved this book! So much more than I was expecting to.
The Curious Incident of the Dog in the Night-time (52)
Dune (51)
The Prince (51)
The Sound and the Fury (51)
Angela's Ashes : a Memoir (51)
The God of Small Things (51)
A People's Kistory of the United States : 1492-Present (51)
Cryptonomicon (50)
Neverwhere (50)
A Confederacy of Dunces (50)
A Short History of Nearly Everything (50)
Dubliners (50)
The Unbearable Lightness of Being (49)
Beloved (49)
Slaughterhouse-Five (49)
The Scarlet Letter (48)
Eats, Shoots & Leaves: The Zero Tolerance Approach to Punctuation (48)
The Mists of Avalon (47)
Oryx and Crake : A Novel (47)
Collapse : How Societies Choose to Fail or Succeed (47)
Cloud Atlas (47)
The Confusion (46) I might finish this one some day, but I dunno. Maybe I should just give it up and find some actual non-fiction about the Royal Society.
Lolita (46)
Persuasion (46)
Northanger Abbey (46)
The Catcher in the Rye (46)
On the Road (46)
The Hunchback of Notre Dame (45)
Freakonomics : A Rogue Economist Explores the Hidden Side of Everything (45)
Zen and the Art of Motorcycle Maintenance : An Inquiry into Values (45)
The Aeneid (45)
Watership Down (44)
Gravity's Rainbow (44)
The Hobbit (44)
In Cold Blood : A True Account of a Multiple Murder and its Consequences (44)
White Teeth (44)
Treasure Island (44)
David Copperfield (44)
The Three Musketeers (44)
Not surprised at how many of these are classics, but I am surprised to see almost all of Neil Gaiman's novels up there. Do lots of people pick his books up on spec and then just never get around to reading them?