As a follow-up to my photo of my Howardian bookcase, I thought I'd show my Lovecraftiana bookcase, which includes not only works by the master, but allied works as well as references and commentaries. The lower shelf (not fully pictured) holds the complete supernatural fiction of the Robert W. Chambers, who of course was one of Lovecraft's inspirations.
Probably the most obscure (though still readily available) volume here is Richard Tierney's Drums of Chaos wherein his historical Sword & Sorcery character, Simon of Gitta, teams up with his pulp sci-fi character John Taggart. Oh yeah--and Jesus makes an appearance. Other more off-beat titles include the flawed but entertaining Shadow's Bend, in which Lovecraft and Howard go on a road-trip to save the world, and Nick Mamatas's Move Underground, which is a Lovecraftian tale as written by Jack Kerouac.
Some of the Chaosium volumes are out-of-print, though, so maybe they're the hardest to come by, these days.