Reelscary accepts public votes on the scariness of films, divided into three different genres of scariness: disturbing, gore and suspense.
1979 classic "Alien" is currently leading the suspense category, with 2008's "Martyrs" taking the gore honors. Hopefully, there'll be sections for books, games and TV shows soon.
See also Where's The Jump?, a public database of scary moments in movies and the quality of said scary moments.