I’m going to be in Germany for 3 months and won’t have ready access to books in English. I want to take with me a couple of real page-turners with enough heft and length to keep me satisfied.
Some lovely long books I’ve enjoyed, so you don’t need to bother recommending:
Lonesome Dove
Shogun
All the Song of Fire and Ice books
Forever Amber
All the Harry Potter books
The Stand
So as you see, I can do Westerns, romance, sci-fi or fantasy. I don’t care as long as it’s GOOD.
Help me out please!
Pillars of the Earth. And if that’s not fat enough, get World Without End, the sequel as well.
The Outlander series by Diana Gabaldon is awesome. It’s a series of 6 (so far) big fat books that run 900-1000+ pages depending on which edition you get. It’s a good mixture of historical fiction, adventure, and romance. The 7th book comes out in September, so you won’t have to wait so long to read the new one if you start now and read fast!
Have you read Dune?
Dune
The Hitch-Hiker’s Guide To The Galaxy: A Trilogy In Five Parts
The Complete Sherlock Holmes
They’re amongst my favourites and they’ll certainly keep you busy for a while! 
I forgot to put these on my already read list. But I enjoyed them (especially Pillars of the Earth).
More like these!
River of Gods, by Ian McDonald; it’s a huge sci-fi novel set in India in the near future.
I’ve tried to read Dune about 4 times. I just can’t get into it. I wish I liked it… but I just don’t.
The Illuminatus Trilogy is a fun romp.
House of Leaves isn’t necessarily long, but it is a bit of a plow through to read everything.
Hmmm… never heard of these… off to research! Thanks for the suggestion!
May I suggest Neal Stephenson’s “The Baroque Cycle”? Three books (in the hardbound version anyway, they split them up for paperback) weighing in around 900 pages each. And a hell of a read.
This.
Bonus points to anyone who might have guessed that I would agree with this recommendation. 
Just a warning on Outlander… it IS a romance. I liked “Forever Amber” and “Pillars of the Earth” (both of which have a romantic thread) but the Outlander series was a bit too much of a bodice-ripper for me to like.
That said, a lot of people love it. I just got a picture of you in Germany for 3 months with nothing but Outlander thinking to yourself “I don’t like romance THAT much!”
The Count of Monte Cristo has been called (and I agree) the best adventure novel ever written. It’s an absolute masterpiece, gripping and engaging on every level. If you’ve never read it, you’re in for a real treat.
I have to disagree about Outlander being a “romance.” Usually people who say that have never read a romance/bodice ripper. Outlander is actually an ANTI romance. Yes, there’s a love story, and sex, but that’s just one facet. It follows absolutely no conventions of romance novels and often does the opposite. Gabaldon has said often that she’d never even read a romance novel when she wrote Outlander. The books actually cross genres – it also has a strong element of historical fiction as well as sci-fi/fantasy; it almost didn’t get published because the publisher couldn’t pigeon-hole it as a single genre.
So yeah, if you don’t like fiction from a female point of view in which there is a love story, skip it. But I will say I know plenty of men who’ve read the series and liked it.
How about The Winds of War or the sequel War and Remembrance? They’re set during World War II and parts of it are set in Germany.
<shrug> It didn’t do it for me, because it spent too much time on the love story, and not enough on the bits that interested me more. And I’ve loved plenty of books that are “fiction from a female point of view in which there is a love story.”
But that’s just me. I just wanted to mention that, since I like a lot of the books the OP lists, and for whatever reason Outlander wouldn’t be the one I’d want to be stuck with for 3 months.
I’d recommend Tom Clancy’s books. His earlier original novels about Jack Ryan that is, not his later ghost-written stuff.
Grab the heaviest Lee Child paperback you can find and enjoy.
I agree, this series is amazing. It will entertain you, make you think, and you’ll learn a lot about a period of history they don’t teach you much about in school.
Another recommendation: The Mists of Avalon, by Marion Zimmer Bradley, which is the Arthurian legend from Morgaine’s point of view. One of my favorites. Also in a fantasy vein, Tigana, by Guy Gavriel Kay.