Grand Unifying Guesses/Warehouse 13

Warehouse 13 is a massive Artifact of Doom collection thus it must have the following in inventory

• Buffy's Scythe-Axe-Stake-Thing, The Hammer used to kick Glory's Ass, An Urn Of Osiris, Acathla, Illyra's casket and a few other things.
• A few Denarii
• Two rusted out, old fashioned revolvers.
• The Ark of the Covenant
• The Necronomicon
• A Shining Trapezohedron
• A Death Note
• The One Ring
• An alien costume
• Horcruxes
• Excalibur
• The Witchblade
• The artifact of Doom
• A puzzle box
• Umbra
• A shard from the Jewel of Four Souls
• The picture of Dorian Gray
  • Confirmed in the fourth episode of the second season.
• Venjix's dormant code and a laptop computer
• A fragment of the Allspark
• The Pandorica
• A chunk of pure smoking hot Evil
• The original weighted Companion Cube.
• A box of Turkish Delight
• A Marker
• The Necroteuch and the Malus Codicum.
• An Anti-Music Missile
• Soul Edge, and the sword forged to counter it, Soul Calibur.
• The T-Virus and all of it's derivatives
• Shinnok's Amulet
• Vendredi's Cursed Antiques
• A Risen Mitten
• Old alien war machines
• A Leprechaun's pot of gold.
• A Delorean (possibly a steam engine train too), and the Flux Capacitor
• A cursed VHS tape
• A Halo Activation Index
• Some pieces of a Reaper.
• The Master Sword
• At least one Keyblade
• The Hakurei Yin-Yang Orbs
• Several rolls of amateur student film.
  • And several more tapes.
  • And camera archives showcasing haunted people.
  • And footage of Operation Hammerdown.
• A Ouija Board
• The Kahili Ring
• The Lance of Longinus
• The Holy Grail
• The Spear of Destiny
• The One True Cross
  • Or at least a fragment of it.
• The African Monolith from '2001: A Space Odyssey'
• The Neverending Story, and the Auryn.
• An Alethiometer.
• A Sangreal.
• A hunk of kryptonite.
  • and a Phantom Zone generator.
• The Jumanji board game.
• The Mask.
• A 1st Edition Dungeons & Dragons manual.
• the Gran Grimoire.
• A piece of the Map of Inifinity
• A certain other mask, only this time holding the power of a demon
  • A mask holding the power of a demon, you say?
• The Hand of Glory.
• A Starmap
• A Prothean Beacon
• The Shiftblade
• A lance and sheild
• A Polybius game
• The Amulet of Yendor
• A rotted hand and eye
• The seven Crystal Stars and the eight Pure Hearts
• A copy of the manuscript for William Shakespeare's Love's Labour's Won
• The Book of the Dead, the Book of Amun-Ra, the Bracelet of Anubis, the Spear of Osiris and the Eye of Shangri-La
• The Philosopher's Stone
• The Witchblade
• A copy of the Sburb beta
• One or more of the Millenium Items
• One or more Dragon Balls
• The script for The King in Yellow (French original, with annotated English translation attached)
• A Tibetan fife
• A bobble-headed devil doll which produces fortunes
• Marvin
• A piece of Unobtanium.
• The "Zoltar Speaks" wishing machine.
• The Émigré Manuscript.
• At least one lantern ring and power battery
• A time lock portal
• A super awesome axe known simply as The Seperator
• The Sword of Omens
• The BFG 9000
• Murray
• the really-really-bad-inator
• A Timing Device
• A golf club that causes people to take up beliefs similar to Ayn Rand's.
• a boomerang
• A piece of Eden
• The Coins of Zakynthos.

Possible future artifacts

• Dick Cheney's shotgun: makes the shooter dangerously innacurate
• Weird Al's accordian
• A syringe belonging to Keith Richards. An injection with it renders the subject immune to all poisons and ill side effects of drugs and narcotics.

Also see: SCP Foundation Grand Unifying Guesses, which Warehouse 13 may be controlled by.