For the sake of clarity, I will define Sci-Fi as not including the vast ocean of sword or magic-related fantasy and other less technological scribbling currently lumped into this genre. I'm looking more towards the hard science fiction of David Brin or cyberspace works like those of William Gibson.
One of my most recent favorites is Peter Hamilton. What's not to like about a book titled, "The Reality Dysfunction"? It is the first of a six-part "trilogy" that was so good I read the entire thing twice. Hamilton has a rare flair for conjuring up really advanced technologies and putting them into a contrastingly mundane framework that propels the plot quite nicely. Many lesser authors would make a centerpiece out of the stuff that Hamilton weaves into the routine backdrop of his stories.
"The Time Ships", Stephen Baxter's pastiche of H.G. Wells' "The Time Machine", was rather impressive but his other works like "Vacuum Diagrams" are sufficiently uneven as to leave me less than happy with his output.
David Feintuch's "Midshipman's Hope" series was a nice enough space opera romp to be worth reading a second time but does not qualify as work on a par with Hamilton's. I am eagerly awaiting the softbound publication of Hamilton's "The Temporal Void", another installment in the Commonwealth series that began with "Pandora's Star".
Incidentally, was I the only one who was less than impressed with Brin's second uplift series that began with "Brightness Reef"? I found it to be overly convoluted and without the strong and relatively linear plot that frequently characterizes his other works. Despite its contorted ending, I especially liked his novel "Kiln People". The implications of having quasi-conscious self replicas was a stimulating challenge in terms of innovative plot lines.
Another pleasant surprise was the add-on "Dune" books by Frank Herbert's son, Brian, and co-author Kevin Anderson. The collection managed to tie up just enough loose ends from the original series whereby they justified their own existence quite adequately.
So, please feel free to recommend other capable science fiction writers that have managed to cobble up truly entertaining alternative realities. I usually stick to the masters, such as Asimov, Clarke, Pohl and whatnot, so my expectations are rather high. Among some of my favorites were the collaborations by Frederick Pohl and C.M. Kornbluth. Their incredibly cynical and outlandish scenarios never failed to amuse.