DUNE!
By far the best sci-fi series ever written. I've read them ALL (those written by Frank Herbert and his son, Brian) several times. I will say that they are very vocabulary intensive, but well worth the time to figure things out. Definitly the coolest and most diverse universe created. I will say that the Brian Herbert books are a very different style, but are an easier read and still enjoyable. Make sure you read them in ths correct order, though, or you'll be hella confused. They span about 20,000 years of human history (or possible future, I guess)
ALL of these books are well worth the time to read.
I'm such a nerd!