It's all very, very good stuff. But Howard did more than just Conan, of course -- he was also the one who created the character of Kull (actually an early version of Conan) and unless I am much mistaken, he may have done a very small amount of stuff in the "hardboiled detective" genre, as well.
Now, the elements of the Kull and Conan stories that deal with magic, gods and other supernatural miscellenaea draw more or less from Lovecraft's mythos. Lovecraft is probably best known for creating Cthulhu and the Necronomicon (which is
not -- and never was -- anything but a fictional device created by Lovecraft, despite rabid fanwank dribblings and an incredibly cheeze-tastic trade paperback, circa 1973, to the contrary.) I've several good recommendations for starter material, but I'll warn you now that Lovecraft's typical writing voice takes a bit of getting used to at first -- I can't think of a better word to describe his prose than to say that it's
rich, in the same way that some foods are
rich. Maybe another good word for it is
thick. It doesn't help that the language he used was a touch anachronistic in places, even for the early 20th century. Regardless of your reading level, you may find yourself hitting a dictionary from time to time -- but it's worth it, and good for you besides.
Now, the recommendations:
Quick reads:
1.
The Other Gods
2.
The Cats Of Ulthar
3.
Pickman's Model (Particularly good.)
4.
Nyarlathotep (Probably the best of the short stuff.)
More in-depth stuff:
1.
At The Mountains Of Madness (One of his best long works.)
2.
The Festival (Also excellent, and IIRC where he introduces the "Necronomicon" for the first time.)
3.
The Dunwich Horror
He's also done a few poems, but I don't have too much longer to spend on this post, so have a google for one called "Nathicana." It's every bit as good as Poe's "The Raven", IMO.
Now, none of these is exactly groundbreaking by today's standards -- but, of course, that's because these works influenced those who helped to
create today's standards. There's a lineage in modern fiction, just as with any other art form, and in the horror/supernatural genres (the American branch, anyway), that lineage most directly goes from Poe, to Lovecraft, then to King. I'll tell you something with absolute confidence and sincerity -- I intend to be the next one in that line, and I fully believe I've the literary chops to do it.
.