Hello all. It's been a while.
I haven't read enough of Lovecraft's poetry to make a qualified suggestion, but as far as fiction goes I would say:
The Colour Out of Space, The Outsider, The Quest of Iranon, The Cats of Ulthar, The Call of Cthulhu, Ibid, The Case of Charles Dexter Ward, Dagon, and The Dunwhich Horror. I might add "The Shadow Out of Time" as well.
I think this would a pretty good cross-section of his work, with a bit of humor, straight horror, fantasy and, of course, classic Lovecraft.