Because of this thread, I found out that my DH had never read Good Omens, a book I thoroughly love! I have now gotten him his own copy, so he can see what all the fuss is about himself!
For myself, I would have to say that my favorite book of all time is A Brave New World. I love how happy most people really seem to be. In most dystopias, there's a sense that people aren't really happy, or aren't supposed to be happy. I liked how frustrated John and Bernard get as they try to explain to people why they shouldn't be happy - that's how I've always thought it would happen.
If I could nominate a series, or a collection of short stories, or an anthology, my choice would be very different. I love the Miles Vorkosigan and Honor Harrington series. I also love almost every Sherlock Holmes story, takeoff, pastiche, etc ever published, but specifically the ones by Laurie King.