See also:
The Holy Grail
Parsifal
Perceval
Parzival
Parzifal
Arthurian legends
The Fisher King
Lady of the Lake
Grail maidens
The Lance of Longinus / Spear of Destiny / Holy Lance: The spear which supposedly pierced Jesus’ side during the crucifixion, reputed to have all kinds of crazy powers ranging from healing to the ability to destroy the whole world in one shot. Three known items are sometimes claimed to be the Holy Lance; One resides in the Vatican, one in the Hofburg Museum in Vienna (having been moved from Nuremberg during the Napoleonic Wars) and one in Krakow, Poland. The Catholic Church has made no statements as to the authenticity of any of them — perhaps wisely as the latter two have been shown by recent research to be of a later origin.
Excalibur is the prototypical “special sword”. It may be called “The Sword In The Stone” which often has purists in a tiff; sometimes Excalibur and the Sword In The Stone are different swords, sometimes they’re the same sword. Arthurian legend is a very sketchy canon. Occasionally called Caliburn from the (possibly original) Welsh name Caledfwlch (pronounced Cal-ed-voolkh, roughly). It’s rarely called that, because Caledfwlch is hard to pronounce and looks rather scarily Welsh.
Less frequently, you will see other legendary Western swords such as Cortana (which actually exists as part of the Regalia of Great Britain), or Joyeuse. However, Excalibur has dozens of appearances for every time one of the others shows up.
Joyeuse is said to contain the Lance of Longinius within its pommel.
The Four Treasures of Ireland: the Lance, Cauldron, the Sword, and the Stone — which pretty much fulfill the same role as the Treasures of Amaterasu do, but for a Western audience. They are sometimes matched up with the four western elements. The Cauldron is often identified with the Holy Grail. It also gets mixed up with the Cauldron of Cerridwen from Welsh mythology and the Black Cauldron. The Lance gets identified with the Spear of Destiny. The Stone is sometimes said to be the Stone of Scone, once part of the Coronation Chair in Westminster Abbey but now housed in Edinburgh Castle.
There are two public domain artifacts associated with King Arthur: Excalibur, which is part of the early legends, and the Holy Grail, an addition which came to dominate the late medieval version of the myth, though it is often excised in modern works. The only magic power Excalibur was ever traditionally accredited with was glowing brightly, and that not always, but the scabbard was said to stop the wearer bleeding, making it fairly useful on the battlefield. There are also two origins to Excalibur, one stating it is the Sword in the Stone that King Arthur pulled that proved he was King, and another stating that he received it from a surprisingly benign member of The Fair Folk, the Lady of the Lake.
Arthurian legend has The Four Hallows of the Fisher King’s castle: the chalice, the sword, the spear (staff) and a platter, which fills the same role as the pentacle. This in turn is derived from the pre-christian Celtic tale of the four treasures of the Tuatha De Danaan, which is sometimes referenced in celtic-themed fiction, for example four treasures of the novel Elidor.