Rendevous With Rama
and the Odyssey
series by Arthur C Clarke (well, anything by ACC, actually).
series by Isaac Asimov.
by Robert Heinlein, as well as just about anything else he wrote.
by Larry Niven (and the sequels, if you like the original).
by Vernor Vinge, especially "Marooned In Realtime."
by Jack McDevitt, and the rest of the Patricia Hutchins series as well.
by James Schmitz, and any other Hub-related stories as well.