Probably most people have seen "The Ring", but have you seen "Ringu"--the original Japanese film on which "The Ring" was based? This is some seriously messed up sh*t--truly disturbing and scarier and darker in every way. Also, the plot is significantly different, probably because an American version couldn't have incorporated some of the geographical/cultural elements of the original.
Atmospheric, wonderful performances, and a mystery that keeps you engaged throughout the entire film. Cons: A few things are hard to buy in terms of storyline, I wouldn't say they lead to plotholes, but certainly believability wanes. Also, in terms of how scary it is, it really depends on what you think is frightening or not.