Science fiction books similiar to the "dune" series?

It is my friends birthday and i am not sure what dune books he has i was wanting to buy him a book similiar on the science fiction genre any ideas?
Answer
Hi there. depends what you mean by similar! for breadth of vision and human striving, the first 4 dorsai books by gordon r dickson. for narrative power and high adventure, harry harrisons "deathworld" trilogy. for mystic eloquence and depth of emotion, "the true game" trilogy by sherri tepper. all have a slice of dune, but not the same - you are asking about one of the few unbeaten classics!. only anne mccaffreys first 8 "dragon" books really compare (may she be forgiven for all the books that followed..) if you will consider fantasy with a hard sci-fi edge, try the ten "amber" books by roger zelazny, available in two volumes. nice luck, steve.