I'm going to go mostly by my gut today rather than page counts, given varying editions and font sizes/spacing, in part to make this more interesting.
The Ones Everyone Knows
1. The whole friggin' Twilight series (they weren't so bad while reading them, but now I'm back to immediately being like WHY when I see their daunting page counts)
2. Certain Harry Potter books who know who they are (...which is PERFECTLY FINE because mega-long book 5 is my actualfax favorite)
3. David Copperfield - Charles Dickens
4. Our Mutual Friend - Charles Dickens (thank u beloved English professor, without whose amazing class and ability to make everything BritLit related fun I would never even have attempted either of the above)
5. Crime & Punishment - Fyodor Dostoyevsky (no thanks @ the AP Lit test for endorsing this as a good book for my teacher to have us study)
Some Other Super Sagas
6. The Amazing Adventures of Kavalier and Clay - Michael Chabon
7. The Lake House - Kate Morton (it's 500 pages and it definitely took me a fair number of hours, certainly beyond the 2-3 most books take)
8. Winner - Maureen O'Donoghue (another all nighter)
9. The Unexpected Everything - Morgan Matson (according to Goodreads, anyway, this is the longest of her books. None of which are short or even of average length for YA)
10. The Miseducation of Cameron Post -- Emily Danforth (and I regret nothing! I recommend this so much; its only flaws to me were the R-rated aspects)
11. The Inkheart trilogy - Cornelia Funke (the font isn't especially small, but...MAN did I forget how long those are, page-count-wise. That is some Twilight rivalin', except I feel the exact opposite when I think about rereading them, as in "what an adventure that would be!")
12. Fangirl - Rainbow Rowell
OK...NOW I'm stopping.