Card, when he’s good, is extremely good. The entire Ender series is just great. There are currently six books in the series with (as of now, at least) two more planned. Three of the six rank among my all-time favorites, and the other three are still pretty good.
Stephenson in my opinion keeps getting better, and he wasn’t bad to start out with. As mentioned before Cryptonomicon isn’t really science fiction but is well worth reading, and I think it’s his best to date.
Brin can be pretty good, but there’s a lot of his stuff I haven’t read yet.
The original Dune by Frank Herbert was fantastic, but a bit of a nit-pick given the OP: he’s dead! And the buzz on the Dune books published after his death is not good at all!
I usually don’t like my science fiction “hard”, but recently I’ve been reading David Weber’s Honor Harrington books, which are oddly addictive. I picked them up because they’re something of a tribute to Forester’s Hornblower books, which I adore. I generally dislike what my friends call “miliporn” - science fiction chock full of details on missile pods and troop deployment and order of battle, but these are character-driven enough to appeal to me. Although if your name isn’t Honor Harrington, don’t get too attatched to life in a David Weber book.
Otherwise, I very much second Neal Stephenson and Stephen Donaldson, and would like to add C.S. Friedman, a lot of whose work reads like fantasy but is all (I think) technically science fiction, and Susan Matthews’ books about Andrej the inquisitioner.