Just read Dune, Dune Messiah, Children of Dune, God Emperor of Dune, Heretics of Dune, and Chapterhouse: Dune. They're the ones written by Frank Herbert.

Although, to be frank, I think you can just stop after Children of Dune and be fine. Dune Messiah is pretty good, Children of Dune is okay, but the rest get progressively weirder and weirder. I'm not a big fan of worm-Leto II, or whatever the hell he was supposed to be in the last few novels.

I haven't read any of the Kevin J. Anderson Dune novels, nor do I plan to. I've heard far too many absolutely awful things about them.

Though Hunters of Dune and Sandworms of Dune together form a sequel to Chapterhouse: Dune that is supposedly based on a 30-page outline by Frank Herbert, I can't see them being any better than Chapterhouse, which I really didn't like.