Hi,
It's odd that when asked about 'hard' SF nobody has mentioned anything by Fred Hoyle:
- The black Cloud.
- The Inferno.
Not that I like very much his style (it's rather poor when it comes to human beings interaction), but hey, it's hard SF.
I agree that R. L. Forward is probably the best hard SF writer by far (much better than Isaac Asimov and Arthur C. Clarke, IMHO).
Not hard-tech SF but 'hard-social SF' there is:
- Camp Concentration, by Thomas M. Disch... I simply love this book.
Aside from that and as everybody is throwing away whatever comes
...
- Red Thunder, by John Varley (Titan is rather good too).
- The Wooden Ships trilogy, by Bob Shaw.
- The Tschai books, by Jack Vance... all right, it's more fantasy and kaboom! than anything but it as enjoyable as any other pulp-fiction book.
Gus.