I've recently read a few of Charles Stross's Laundry series of books. These obviously reference Lovecraft in many ways but-- since I've never read any Lovecraft -- I don't know which stories are most relevant here. Which Lovecraft stories would be best for someone familiar with the Laundry series who'd like to begin exploring Lovecraft's work?
You can get the complete Lovecraft ebook.
The Complete Works of H.P. Lovecraft contains all the original stories which Lovecraft wrote as an adult. It begins in 1917 with “The Tomb” and ends in 1935 with his last original work “The Haunter of the Dark.” The book is ordered chronologically by the date the story was written.
I would start on page one and continue onwards. The closest to the Laundry in Lovecraft's works would be encountering BLUE HADES in The Shadow Over Innsmouth, Shoggoth (Yes, I cannot remember the codename for them, please edit if you do) appear in At The Mountains Of Madness, and the whole concept of cosmic hopelessness.
The Cthulu Mythos of Lovecraft. The Laundry doesnt directly reference any of Lovecrafts work though.
Since I wrote the above details, the short story Equoids by Charles Stross has come out (its free to read on the TOR website http://www.tor.com/stories/2013/09/equoid). The story directly references Lovecraft (that old fraud as the character Bob refers to him) and some letters that Lovecraft wrote...