I personally love the entire series of Dune books. Dune Messiah and Children of Dune are very good. But it gets very weird in God Emperor of Dune and that continues through Chapterhouse: Dune. I personally don't mind the weirdness but it turns some people off. But, beyond the original book, there are many side stories and prequels done by Frank Herbert's son, Brian Herbert and Kevin J. Anderson that don't include the weirdness of the later Herbert books. The Herbert/Anderson books aren't quite as "deep" as what Frank Herbert wrote, but it's still a good set of stories in a very interesting universe.
If you are looking for hard Sci-Fi, Alastair Reynolds. For more space opera stuff, check on the Empire of Man Series by David Weber and John Ringo. Also the Safehold series by David Weber.
I'm also a huge fan of Neil Stephenson. He crosses lots of genres but his most famous stuff if mostly Cyber Punk. i.e. Snow Crash, The Diamond Age. But, I'm a big fan of all of his work including the Baroque Cycle series, Cryptonomicon, Anathem, and Seveneves.