I would recommend anything by the Big Three (Asimov, Clarke, Heinlein). For me, they can do no wrong, but these sort of things are relative.
The last 4 book I have read i've enjoyed, some more than others, but I would recommend them all
Clarke- RENDEZVOUS WITH RAMA
I re-read this when I heard of his death. This is a classic of the golden age of sci-fi, because it's plot is centered in the mystery of exploring new worlds, it doesn't have lot of action but it's really interesting to read a story where an object is the main character. One of Clarke's must read books.
H.P. Lovecraft-Black Seas of Infinity
For any lover of horror/fantasy fiction this is truly a great selection. This book contains some of Lovecrafts greatest works, and is a great starting place for anyone who has never had the enjoyment of reading Lovecrat's fiction.
Frank Herbert- Dune
Firstly, This book puts the movies to shame (and i'm a big David Lynch fan )This Book is a must have of any science fiction library. The story is timeless and everyone should read Dune at least once. After I had read this, I went to Amazon to order the next 4 books in the series.
Richard Paul Russo-Ship of Fools
Think of any haunted house movie you've seen, only, it's in space. With Predators (kinda). Really good ending, I thought.
Right now I am reading I, Asimov. A memoir.
Hope this helps