The Internet Movie Database (IMDB.com) has put together a list of the Top 10 Horror Movies. It's based on votes and ratings from IMDB users; so there are a lot of movies you don't see on most Top 10 horror movie lists:
#1.) "The Shining", 1980
#2.) "Alien", 1979
#3.) "Shaun of the Dead", 2004
#4.) "Psycho", 1960
#5.) "Cloverfield", 2008
#6.) "Zombieland", 2009
#7.) "Saw", 2004
#8.) "The Exorcist", 1973
#9.) "28 Days Later", 2002
#10.) "Sweeney Todd", 2007