If you have seen any reasonably decent adaptations, do share.
The Unnamabale was actually really good. It's not necesarrily supposed to be an outright horror though. They showed that one at the last H.P. Lovecraft film fest I was at, if I remember correctly they even had the director and the main character as guest speakers.
The two movies by The H.P. Lovecraft Historicle Society,
http://www.cthulhulives.org/ are really well done. The Call of Cthulhu,
http://www.cthulhulives.org/cocmovie/ And The Whisperer in the Darkness,
http://www.cthulhulives.org/whisperer/They also have what is called The Dark Adventure Radio Theature which is done in the style of old radio programs and those are also really good, picked up the Octopack which has all eight that are currently out.
http://www.cthulhulives.org/store/store.lasso I listen to those when I am on a long drive.