I don’t know if I’d call it horror, but have you read any of Ruthanna Emrys’s stories about the next generation of the Deep Ones? Amazon has them, and I think they’re rather good.
I would recommend both the Howard and the Emrys, as well as David Hambling’s The Elder Ice and sequels, and Sarah Monette’s excellent collection The Bone Key. There’s a “lovecraftiana” tag on my blog under which all of these are reviewed.