Frankenfish (2004) - A genetically modified "fish" has been killing people and two experts are dispatched by law enforcement to research and investigate the cause of the latest fisherman's death. You can watch it for free here.
Dagon (2001) - Directed by Stuart Gordon and written by Dennis Paoli, this flick was actually based on H. P. Lovecraft's novella, "The Shadow Over Innsmouth", rather than his earlier short story "Dagon" (1919). In fact, the setting takes place in 'Inboca' is a Spanish adaption of 'Innsmouth'.
The actual Dagon short story is the testament of a tortured, morphine-addicted man who plans to commit suicide over an incident that occurred early on in World War I when he was a merchant marine officer.
You can watch Dagon below.
The Call of the Cthulhu (2005) - The sailors aboard the Emma first encounter the Alert abandoned at sea, rather than crewed by Cthulhu cultists and taken over by Emma's crew after a violent confrontation as in the original story. Additionally, the film depicts the narrator present at the time of his great-uncle's death, who dies peacefully in his sleep, rather than being summoned upon the mysterious death of his great-uncle, who was presumably killed by Cthulhu cultists in the original short story.
The narrator notes as well that Inspector Legrasse, who had directed the raid on cultists in backwoods Louisiana, had died before the narrator's investigation began.
In the original story, the narrator does not seem to end in a lunatic asylum or experience any mysterious nightmares himself. Its shot in black and white and given the mood as if it was shot long ago despite the fact that its a relatively "new" film.
To view this free, short (47 minutes) Lovecraft-based flick click here.