I love to find the quirky, non-mainstreamed, but really excellent Horror movies to add to my collection. So I want to know what are some of the essentials on DVD that I should own?

I would consider mainstream something like "Halloween" and non-mainstream essential like "Ginger Snaps" (something with cred. not on the beaten path)

So what are the essential others that I know are out there and I have no clue about?

Black Christmas, Basket Case, Toxic Avenger, Audition, Uzumaki, Bad Taste, Bio Zombie, Blood for Dracula, Martin, Re-Animator, The Curse of Frankenstein, The Devil's Backbone, The Giallo Collection, The Hills Have Eyes, I Spit On Your Grave, Kairo, Killer Klowns From Outer Space, Night of the Demons, Tenebre, Patrick, Patrick Still Lives, Prince of Darkness, Santa Sangre, Sleepaway Camp, Demon Knight, Suspiria, Deep Red, Torso, Versus, Two Evil Eyes, The Wicker Man, What Have You Done to Solange?

Audition (Japanese), available on R1 dvd.
A Tale Of Two Sisters (Korean), available on R3Korean and R3HongKong.
Probably the two most disturbing moders horror films I've seen.

Edit:
And pretty much everything MahatmaPetey recommended.

I really enjoyed Slashers, though obviously it wouldn't be everyone's cup of tea.

Dog Soldiers was good.

Just saw The Bunker. Don't know if that's highly regarded or not, but it was interesting. Not my favorite, however.

I'm waiting to watch Near Dark, which got some accolaids.

Of course, these are all rather new movies. If you want all-time stuff then there's a lot of ground to cover.

I'm so glad you specified that you wanted us to name the titles. I was just gonna list the names of the second unit assistant gaffers and hope you recognized the films based on that.

Check out My Little Eye.

The Hicther
Brain Damage
God Told Me To
Hitch Hike
April fools Day
Blue Sunshine
Fright Night
Beyond the Darkness
Daughters of Darkness
The Flesh and the Fiends
The Grapes of Death
Horror Express
Jungle Holocaust
Vampyres
Let Sleeping Corpses Lie
Monkey Shines
The Crazies
Q: The Winged Serpent
Nosferatu ('79)
The Brood

Prince of Darkness many would prob disagree, but I think this is John Carpenters scariest film ever - freaks the hell out of me, if you have not seen it yet, pick it up.

The Eye Although the movie gets stale about half way through, there are a handfull of excellent scares in the first half

Session 9 is the only one I can think of that is yet to be mentioned.

If you liked Ginger Snaps then get Ginger Snaps 2 Unleashed for some more Fitzgerald sister mayhem.

Visitor Q is pretty much off the beaten track.

Last House on the Left is disturbing.

I Drink Your Blood.