I'm a HUGE HUGE horror movie buff, and The Ring is one of the scariest yet. I watch all my horror movies at night with the lights off and headphones though, so the atmosphere is more conducive to it. The original Japanese was maybe even scarier (only because i watched it before the American version), but i found it had a lot more holes than the American version... but if you watch all 3 of the Japanese one (Ringu, Ringu 2, Birthday (prequel to all 3, but watch them in that order)), then it makes sense. Trust me, in the right atmosphere, The Ring is one scary movie. I had trouble sleeping for 2-3 days, and i've seen probably every single horror movie that has ever been made and worth watching.
On the other hand, the new Dreamcatcher by Stephen King blows. I'm not even sure what to categorize it as, but it definitely isn't horror.