Anything by Robert Heinlein, (except Puppet masters, I saw the beginning of the movie and it creeped me out

)
Douglas Adams "Hitchhikers guide to the Galaxy" Any of the Harry Turtledove "alternate histories" (Guns of the South )
David Drake, Can't think of any more off hand but there are several in the Sci Fi war genre that are good, like David Weber's "Honor Harrington " series.