Not individual books, but series.
  1. The Wheel of Time (series) by Robert Jordan
    If you're not familiar, get familiar. Such an amazing series, somewhat similar to LOTR, but very much it's own universe.
  2. The Lord Of The Rings Trilogy by Tolkien
    Who wouldn't?
  3. I haven't read as much as I should've the past few years, this is a tad difficult.
  4. The original Halo book series by (mostly) Eric Nylund
    I'm a bit of a video game nerd and I love everything about the Halo universe.