My favorite author is probably George R. R. Martin. He creates amazing, complex characters that you just get so caught up with, whether you love them or hate them. His works run the gamut of popular fiction - the "A Song of Ice and Fire" series for fantasy, Tuf Voyaging and Dying of the Light for sci-fi, Fevre Dream for horror, the Armageddon Rag for modern day (with a touch of fantasy I guess), all amazing works.
Another favorite is Neil Gaiman, the master of modern day fantasy. His prose is beautifully poetic, and just so imaginative - reading him just evokes this sense of wonder like no one else can.
Another author worth mentioning is Jeff VanDerMeer - his work is just so unique. I'm having trouble in explaining it... just go out and read "City of Saints and Madmen"