Who Goes There? by John W. Campbell Jr.

 Using simple words along with a simple, but interesting plot, this book makes writing a great story seem easy. The author never took the easy way out, instead at every turn the monster proved to be perfect in its ability to kill and assimilate into the group. Plans that would have worked in the hands of other authors instead failed miserably. The book never feels dated, but instead feels as if it could have been published yesterday.

I would recommend this book to anyone.