My hands-down favorite is the Gateway series, written by the one and only Frederick Pohl. The complete list of his writings is here on his
website:
www.frederikpohl.com...
It's very hard to believe that Gateway was written in 1977 (!) because it contains the most accurate descriptions of online avatars, even counting
the current day, that I have ever seen. In-credible.
Another remarkable achievement: Gateway and its successor novel both contain amazingly prescient descriptions of global terrorism. How about that?
Runner-ups would have to include the Giants series by James P. Hogan, whose website is:
www.jamesphogan.com...
Also the Known Space series written by Larry Niven, whose fan-run website is:
www.larryniven.org...
So what are your favorites?