Some of my personal favorites are Re-animator, From Beyond, The Howling, House of 1000 corpses, The Thing(1982), The Toxic Avenger, Slither, Return of the Living Dead, and Alien.
One of my most favorite scenes here------->
http://www.youtube.com/watch?v=Ql4Ooz95ulU
*As far as modern horror, well that's why I started writing. It's gotten to violent and beyond any logical reason. My goal is to bring back smart horror and that's why I write and choose to stay independent.
Slither is one of the few modern horror films I like. IMHO, horror died when artists gave up real time creature effects for CGI.
*Another great film is the original REC and REC2. Those are spanish, I think, not sure but I think that's correct. Those films were blatantly ripped of by Quarantine but fell into copyright limbo.