My first H.P. Lovecraft purchases were the Del Rey paperbacks. Nothing has ever come close to Michael Whelan's "Lovecraft's Nightmare" diptych that he did for the covers of those books. Just black, white, and red, the paintings are evocative rather than literal interpretations of HPL's stories. Some of the 60s and 70s pulp paperbacks had trippy covers (I got one from the library that featured Brown Jenkin and it was unsettling) but nothing like Whelan's. Do you have any favorite covers?