Deception Point by Dan Brown. I started it at Christmas.. and I still haven't finished it. I really need to get around to reading it again.. I always get distracted by other books.
There's The Host by S. Meyer too. I started that at Christmas too... not even half way yet; again, got distracted.
Don Quixote by Miguel de Cervantes took me months to read. At the time, it was a little bit above my reading level, so I kept putting of finishing it. I'm glad I eventually read the whole thing. It was a great book.