Below are two covers for Arkham House editions of Lovecraft's work. The artist for these two covers was Lee Brown Coye.
At the Mountains of Madness by H.P. Lovecraft. Arkham House, 1964.
Dagon and other Macabre Tales by H.P. Lovecraft. Arkham House, 1965.
The book below, with a cover by an unknown artist, was distributed through Scholastic Book catalogs given to grade school kids in the 1960's and 1970's. This book served as an introduction to H.P. Lovecraft for many children of that time period.
The Shadow Over Innsmouth, by H.P. Lovecraft. Scholastic Books, 1971.
After we had gotten the above Scholastic book and been freaked out by it in the sixth grade, we went to the local bookstore and probably found one of these volumes with the disturbing covers by John Holmes.
At the Mountains of Madness, by H.P. Lovecraft. Ballantine Books, 1971.
A poorly-rendered, pulpesque zombie graced the cover of this Avon edition:
Cry Horror! by H.P. Lovecraft. Avon Books, 1959.
Not by H.P. Lovecraft, but this volume by Brian Lumley contains tales of the Cthulu Mythos and sports a nice cover by Stephen Fabian.
The Horror at Oakdeene & Others, by Brian Lumley. Arkham House, 1977.
I couldn't resist one more by Lumley. This one features some very early art by Michael Whelan.
The Transition of Titus Crow, by Brian Lumley. Daw Books, 1975.