Recommending Lovecraft to novices is a bit tricky, since, well, he wasn't a very good writer. Not to mention that he had some rather unpalatable opinions about race that show up occasionally. What he did better than anyone else at the time, though, was come up with ideas; he created this entire shared 'verse in which the horror comes from people gradually discovering that they're just tiny little cogs in a world that's much older and much more populated than we think - and that we are as ants to most things in it.(Basically, the BtVS backstory - once demon roamed the earth and they still wait underground - is pure Lovecraft, if a bit tamed.) The horror in Lovecraft isn't that you might get eaten, the horror is in that huge gaping chasm between what we think we know and control, and the realisation that we know NOTHING and our entire well-ordered man-on-top philosophy is maddeningly naive...

Anyway, recommendations are also tricky since he almost exclusively wrote short stories with a few novellas interspersed. I'd say the best recommendation is to find a story collection that includes "The Shadow Over Innsmouth", "The Color Out of Space", "The Call of Cthulhu", "At the Mountains of Madness" (novella), "The Nameless City", "Rats in the Walls", "Imprisoned with the Pharaohs", "The Dunwich Horror", "Pickman's Model" and a bunch of others and dive in. If you read e-books, his works are all in the public domain so you should be able to find them for free on gutenberg.org and other sites.