I don't know if you'd call it a novel exactly, but 1001 Nights is extremely interesting. Also, War and Peace, like others have been saying. Ulysses, Middlemarch, Moby Dick, all pretty great.
Aaaaaand pretty much any other suggestions I had are either already on the list or - you guessed it - fantasy. Book of the New Sun I can heartily recommend to anyone who does like fantasy and long books though.
Kudos on finishing In Search of Lost Time, I'm still halfway through the second volume, but someday... I read Crime and Punishment too, great book. I still need to read the rest of Dostoevsky's work - which would make a good suggestion for this thread actually - read Devils/Demons/whateverthefuckit'scalledinyouredition, The Idiot, and The Brothers Karamazov (and Notes from Underground too, though it's actually very short).
Also, since you didn't actually specify fiction, I often find just reading massive books about history to be interesting - Norman Davies' Europe: A History, for example. Probably not what you were looking for though.
Oh and if you happened to be interested in poetry, The Maximus Poems by Olson are an excellent, and very very long, series of poems.
octafish said:
Stop fucking about with this little stuff. Remembrance of Things Past AKA In Search of Lost Time. Marcel Proust. Get back to us when you finish that. One Novel. Seven Volumes. You can read the English translation if you like.
Maybe read the OP next time.