I read Infinite Jest. 1079 pages, but I enjoyed every last one. Okay, there were some pages that were a kind of boring, where I couldn’t wait to get back to what was happening at the tennis academy, but it was a really good book.
I’ve read Ian Kershaw’s biography of Hitler. If you count both volumes as one book, it works out about 1650 pages, if memory serves.
The Illuminatus Trilogy (one book) comes in at well over a 1000 pages. fucking hard book to get into as well, jumping between characters in the same paragraph to start with.
LOTR I consider 1 book.
done plenty of 5-700 pagers. normally takes about 2-3 weeks for those.
Arthur C. Clarkes Rama series must be 2000+, but thats not really 1 book.
The Spanish Civil War by Hugh Thomas - 1136 pages.
I did finish Marcel Proust’s A la recherche du temps perdu/Remembrance of things past while commuting. The french Gallimard pocket edition adds up to 420 + 514 + 578 + 515 + 399 + 273 + 353 = 3052 pages.
I’m thinking of reading it again because I seem to have forgotten half of it. Still I’m not sure whether the feeling at the end is one of joy at the great book you’ve read or sheer relief that it is finally over. 
And, though it’s been said endings have never quite been his strong point, I really get the impression this is the first volume of a big book not a book in a trilogy.
Do textbooks count? Glancing at my bookshelf I see “Mathematical Methods of Physics and Engineering” is about 1000. Further, most textbooks are probably heavier going than most fiction, however dense: stopping to cover a piece of A-4 in scribblings every sub-clause is time consuming 
Like others have mentioned, a Suitable Boy, It, LOTR, The Stand, and the Quran.
For me, it’s probably the last book in the Memory, Sorrow, Thorn trilogy, which is called To Green Angel Tower. In paper back, it had to be split into 2 books, which according to Amazon are 816 pages each. That makes the whole book 1632 pages.
The borrowed version of the Illuminatus! I read clocked in around 1000 pages.
I got a good way into a translation of The Water Margin that ran about 1200 pages before I had to quit due to college classwork.
Everything else I can remember right off falls short of the 1000+ standard established, lots of Niven and Pournelle, Claney, Dumas, etc. in the 600-900 range
The book that seemed the longest was George Eliot’s borefest Silas Marner, inflicted upon my 9th grade Advanced English class. It took so long to get through, the teacher kept bumping back the completion date and the test as she was re-reading it with us.
The most voracious reader I’ve ever known IRL read the entire Battlefield: Earth series (avg. 1000+ pages per book) and declared that they were, “Okay, nothing special.” Seems a long slog for something you consider so underwhelming, but he’s a strange guy.
73 books? Not 66?
What are the other 7?
Tobit
Judith
1 Maccabees
2 Maccabees
Wisdom
Sirach (Ecclesiasticus)
Baruch
If my memory serves, Thea is Byzantine Catholic, and uses the Catholic Bible, which has those seven OT books which are not in the Protestant Bible.
Outlander and its 4 sequels all were well over 1000 pages. Time well spent.
Gone With the Wind
Lonesome Dove
I’d recommend all the above FWIW.
I’m rather suprised no one’s mentioned any James Michener books yet. <i>Chesapeake</i> is one of the longest books I’ve read, at 1024 pages.
<i>Anna Karinina</i> is pretty long; my version is 853 pages and small print. I’ve read some other Michener books and the Lord of the Rings trilogy.
One story (though three books) The Second Chronicles of Thomas Covenant - 1472 pages.
Shogun, paperback 1210 pages.
I ploughed through all six Folio Edition volumes of Edward Gibbons’ “Decline and Fall of the Roman Empire”, a surprisingly easy read. Comes in at 3800 pages according to Amazon - I don’t have my copy out here to check.
Like others I have also succesfully tackled JRRT’s “LotR” and “Silmarillion”, the three volumes of John Julius Norwich’s “Byzantium”, James Clavell’s “Shogun”, Vicram Seths’ “A Suitable Boy” (loved the politics, hated the love story and did not believe in the ending) and some of the “Barchester Towers” series.
“War and Peace” is on the list, but never intend to even try “Ulysses”…
Gallimard published it entirely in one volume that weighs in at 2408 pages a few years ago. Small print too. That’s my record.