I wrote a post about a hardcore military sci-fi series by David Gunn in the book section;

http://simhq.com/forum/ubbthreads.php/topics/2977111/Death_s_Head_David_Gunn.html#Post2977111

I've not seen this author mentioned before and I think he is well worth checking out.

I can't believe in a thread this long about Sci-Fi novels, not one post mentions anything about Poul Anderson. While he is not the household name that his contemporaries became (Ray Bradbury, Arthur C. Clarke and Isaac Asimov), his work was extensive and of comparable quality. Come to think of it, I don't recall seeing Ray Bradbury in any of the previous posts either.

Tau Zero, one of my faves.