[DanBC]

I enjoy Adam Roberts, and he doesn't tend to get much mention on HN. I particularly enjoyed Salt and New Model Army.

I also enjoy Allen Steele, and again he doesn't get much mention on HN. I really enjoyed the Coyete series, although many people get stuck on the lack of science in them.

I don't know about underrated, but I also loved reading Interzone when I was younger, and the anthologies are great if you can get hold of them.