Some which I have re-read recently and still enjoyed:

  William Gibson's Sprawl trilogy

  Frank Herbert's Dune series

  Isaac Asimov's Foundation series

  Frederik Pohl's "Gateway"

  Robert Heinlein's "The Moon is a harsh Mistress"

Some which I remember liking when I read them many years ago as a teenager:

  E.E. Doc Smith's Lensman series

  David Brin's Uplift series

  Peter F. Hamilton's Greg Mandel trilogy and The Night's 

Dawn trilogy

  Orson Scott Card's "Ender's Game"

  George R. Dickson's "Dorsai!"