Gouri,
Did you see Dark Skies? Watched it recently and really dug it. Stuck with me for about 48 hours which is pretty good.
I was incredibly excited to see it. I'm pretty sure I saw this on release day in Hawaii. To me it was... ehh.. Predicable. I like the premise, as I love the concept of alien abduction, but then it seemed like we were on rails for a point, and that the ending was simply unavoidable. I don't like that aspect of the movie, but I do understand it. There were some plot holes though, as I recall. I just wish they had fleshed out the concept a bit better and focused more on either the horror aspect or the aliens.
Watched Mothman Prophecies recently too. Creepy, good atmosphere but the end was somewhat of a let-down. Would have enjoyed seeing more of the Mothman himself or at least hints of him.
Mothman is one that the atmosphere and setting is so intense that it makes up for everything else. The end was a let-down, and the Mothman should have been altered a bit to be something a bit more understandable for the audience. They obviously wanted to keep the idea consistent with that of an urban legend, but I think that's what made the move difficult to get into a points. I'd have rather they simply make a more traditional thriller with a more traditional antagonist.
The ending was very anti-climatic and predictable as well.
If you like those two movies you might wanna watch Fire in the Sky. There's also another movie, a found footage film that's not bad..
As far as some pure horror that deserves mention : Grave Encounters is often overlooked, and it's sequel is criminally overlooked (not as good, but still).
And if you want some trippy as fuck sci-fi movies, try Dark City, 12 Monkeys, and Donnie Darko.
p.s.
If you're on LSD
(and with a sober friend), 2001: A Space Odyssey, Star Trek The Motion Picture, and Dune (unedited Director's cut) are good for a long sci-fi based trip.