I'm going to take some flak for this, but I will list two that probably won't be recommended otherwise:
First of all, George R.R. Martin: He takes a lot of flak for being a 'fantasy' writer, but I fail to see the problem with using a medieval setting myself (which he does in his magnum opus, the A Song of Ice and Fire series) and he is by far one the finest authors I have read and bar none the best character builder. He's the only author I know of that has characters that are actually completely 3-D so to speak, realistic, and that I truly cared about or immensely hated and his world building is fine too, and for the most part quite realistic (elements of magic only pop up occasionally and there are certainly no magic based Deus Ex Machinas going on). A highly under-rated author.
The second would be H.P. Lovecraft who is bar none the best horror writer I have ever read. That man truly understood the nature of fear and played off of it to generate tales that will sink deep into your 'soul' and consciousness and leave you shivering when you recall them months later, rather than simply giving you cheap thrills. His amazing grasp on the English language is quite impressive, too.
