The Forever War by Joe Haldeman (spelling?).
Sci-fi but not in-your-face-crazy-techno-sci-fi. It's got action, romance, adventure, a little politics. It's not cheesy sci-fi either, its very down to earth/gritty, realistic sci-fi, with a lot of intelligent thoughts on how society could potentially change over hundreds, if not thousands, of years.
I'm not a sc-fi nut but this books was GREAT.