My personal all-time favorites are simply all novels done by arthur c clarke, especially Rama 1, 2001 and Ghost from the Grand banks... from other authors i love:
Frank Herbert: Dune (as well as all the novels that are now done by his son.. awesome work to kepp SUCH a project alive!)
Stanislav Lem: Solaris
Tad Williams: Otherland (yet only the first novel..)
John Brunner: The Shockwave Rider
I think I need to move Bujold up to favorite author status, though. She can hold a set of characters together for a rather lengthy set of books...
I have to admit to being a bit of a junky for this type of reading. One of the authors I find easiest to read and that still provides a good story line is Alastair Reynolds.
Read a lot of SF when younger, not much in recent decades.
But there was a compilation of short stories called "The Expert Dreamers", all written by scientists. I particularity remember one story called "On the feasibility of coal fuelled power stations". It was set in the far future when fissionable material was running out and they were looking for alternate fuel sources.
I would have to strongly recommend the Sector General series by James White, especially if you have any interest in medical topics. Very Tolkien-esque like writing of developing an entire "universe" along with a custom classification system for alien species I found fascinating.