Excellent hard SF writer. The books can really get you thinking, which I quite enjoy. I also enjoyed Ian Banks' work, particularly his "Culture" novels.
And then there's Charles Stross. His "Rule 34" (a sequel to "Halting State", but reads nicely on its own) is interesting from a couple points of view. It is written in second person (There's a surprising reason for that...), and none of the characters are straight. For light summer reading his 'fantasy' Merchant's War series is great (and turns some hoary old tropes on their head, as well as not being fantasy at all!), as is his "HP Lovecraft in the IT department" Laundry series.