I just watched Re-Animator yesterday and really liked it. I had watched it before and wasn't too impressed, but Combs is great.
Of this list, In the Mouth of Madness is easily my favorite and most Lovecraftian of them all. It isn't directly based on any story, which I think helps lend to it's loyalty to the Mythos as opposed to trying to stick to a story but straying where necessary. It is an original piece of work all it's own but captures Lovecraft amazingly well.
The Call of Cthulhu and The Whisperer in Darkness adaptations by the HPLHS are quite good, though I still didn't enjoy them as much as I had hoped I would. Whisperer is my favorite story and I really loved elements of the film, but other parts turned me off.
Honestly, I think film has done the worst job in capturing the Lovecraft spirit. Several video games and musical works have done a far better job of putting you in his universe.
As much as I adore Re-Animator... the reasons do not connect with Lovecraft. My answer us bratty- last year an agent sent me the script for AT THE MOUNTAINS OF MADNESS by Guillermo Del Toro & Matthew Robbins, and I want that made. Dammit. (Although it looks like it'll be a go again, so woo hoo.)
Dagon is possibly my favorite, with The Haunted Palace being a close second. l like the two films from the HPLHS, but Whisperer got a little off track towards the end and l felt the overall story wasn't entirely there. Would love to see these guys do something with The Shadow Out of Time.
Alien and John Carpenter's The Thing are still my favorite "Lovecraftian" films, however, and when it comes to fear of the unknown and cosmic dread on screen, these two films will be hard to surpass.
From Beyond, if they had stopped the film just shy of giving the main character some sort of flesh starved brain worm. Re-animator isnt really all that close to love craft aside from the elixir. I cant wait to see if del torro makes a decent mountains of madness movie