This is a Lazarene thread I guess and all the better for that. I don't really have a top five books because they are always being jostled by new discoveries and re-readings. I am delighted and astonished to see someone mentioned Hal Clements Mission of Gravity which I read many years ago and found it full of "hard" science and just enough fiction when I was at a phase that needed that. I recommend it to any late teen science-fiction fan. One book which I reckon I would put in a top five would be The Uttermost Part of the Earth by Bridges. I have recently discovered a brilliant American called Jayne Anne Phillips. Would she knock Nostromo or Voss off their perches in my personal pantheon? Maybe. I unhesitatingly draw attention to her.