Maria went through and analyzed the responses to an older thread about the Best Novel You Ever Read. Her post is a great resource, and it includes the link to the underlying thread -- all 19 pages of it (last updated in June 2012).
http://www.dcurbanmom.com/weblog/2011/07/29/dcum_books
I can't remember if I've added some of my favorites to that list, so here are a few:
(1) The Looming Tower, by Lawrence Wright -- Brilliantly written (and Pulitzer-winning) account of the road to 9/11. Though non-fiction and chock full of history, I found it every bit as engrossing and suspenseful as a novel, but of course heartbreaking on a much deeper level. It's an incredible read!
While I'm thinking about non-fiction, I also really liked David Halberstam's classic "The Best and the Brightest," about Vietnam and his more recent book, "War in a Time of Peace" about foreign policy during the Bush I and Clinton years. Again, it's history but written by a journalist (rather than an academic historian) in a way that makes it as accessible (and dare I say entertaining) as a novel.
(2) Bossypants, by Tina Fey -- Also non-fiction, but completely in the other direction.

Very funny -- entertaining from start to finish, and also smart and insightful. (The audiobook is especially good -- she narrates, and it's like hearing your BFF tell hilarious stories about her life.)
(3) The Time Travellers Wife, by Audrey Niffeneger -- An oldie, but one of my favorites. I don't usually like science fiction of any kind (time travel?!!), but I was completely sucked in to the point where I couldn't put it down and actually cried a few times. (Haven't read her more recent book yet. Thoughts, anyone?)
(4) What Alice Forgot, by Liane Moriarty -- Chick lit at its finest. A quick and light read, but then again more. In addition to enjoying the story, I found myself thinking and reflecting on my own life as the story continued. Good stuff!