Having a Valyrian steel sword is a huge deal in Game of Thrones. Firstly, because ever since the doom of Valyria, the knowledge on how to forge new blades has been lost, thus making any Valyrian Steel in Westeros a treasured family heirloom. They're also extremely important for their usefulness against White Walkers — as fan-favorite Jon Snow learned awhile back:
In the latest episode of Game of Thrones, Sam Tarly leaves his family home in Horn Hill in the possession of Heartsbane, the Tarly's ancestral Valyrian steel sword. While in A Song of Ice and Fire book series there seems to be quite a bit more of the valued steel laying about, in the TV show we haven't seen all that many swords. Considering Winter has (apparently) already come, it's important to know who would be on the winning side in a duel with a White Walker.
These are the blades shown in Game of Thrones so far, their current owners and whereabouts. Take note!
As said before, it belongs to House Tarly and has been in the family for over five hundred years. Since Sam is a Tarly himself, it remains in the family. It is a two-handed great sword with a jeweled scabbard. Randyll Tarly, Samwell's father and Lord of Horn Hill, wielded Heartsbane in Robert's rebellion (where he sided with the Targaryens), and later wore it while supporting King Renly Baratheon in the War of Five Kings.
Whereabouts: Currently on the road with Sam and Gilly, in the Ridge.
The ancestral bastard sword of House Mormont — also for five centuries — it belonged to Lord Jeor Mormont. Upon taking the black and joining the Night's Watch, Jeor passed it on to his son and heir, Ser Jorah Mormont. Later, when Ser Jorah was caught selling poachers into slavery and went into exile, Longclaw was returned to his father at the Wall.
In Season 1, Jon Snow saves Lord Commander Jeor Mormont from a wight, and Jeor gifts him Longclaw. He changes the pommel from a bear — sigil of House Mormont — to a wolf, representing House Stark. Last season, Jon used Longclaw in a fight against a White Walker — the Valyrian steel shattering the Walker upon contact.
Whereabouts: As of Season 06, Episode 05, Longclaw is traveling South from the Wall, still in Jon Snow's possession.
One of the two blades reforged from Ice, the Stark ancestral Valyrian great sword, under the orders of Tywin Lannister. Tywin gave the blade to his son Jamie who, in turn, handed it to Brienne. He charged her to use it to find and protect Sansa Stark, and Brienne named it Oathkeeper — in reference to the oath she swore to Catylin Stark.
Whereabouts: Oathkeeper and Brienne are bound to Riverrun, at Sansa's command, to enlist the help of Brynden "Blackfish" Tully in retaking the North.
The second and smaller blade reforged from Ice, presented by Tywin Lannister to his grandson King Joffrey, as a wedding gift. The name Widow's Wail came as a suggestion from an unnamed guest at his pre-wedding breakfast, but Joffrey decided to keep the name, because it reminded him of Ned Stark's beheading.
Whereabouts: When Joffrey died at the Purple Wedding, Widow's Wail passed on to his younger brother Tommen.
Back in the first season, Bran survived an assassination attempt in Winterfell. The hired assassin wielded a dagger made of Valyrian steel and a dragonbone handle. Upon investigation, Catylin discovered the blade belonged to Petyr Baelish, who claimed he had lost it to Tyrion Lannister on a tournament bet. The dagger is later seen on Eddard Stark's table, while he was acting as Hand of the King.
Whereabouts: It is presumably in the keep of Petyr Baelish.
BONUS: Dark Sister
Dark Sister is one of the two ancestral swords of House Targaryen — the other being Blackfyre. It was wielded by Visenya Targaryen, the elder sister of Aegon the Conqueror. Dark Sister was passed down through Targaryen generations, until it ended up with the legitimized bastard son of King Aegon IV, Brynden Rivers a.k.a. Bloodraven.
Brynden was the Hand of two kings and later, Lord Commander of the Night's Watch. It is said he took Dark Sister with him to the Wall. He disappeared beyond the Wall on a ranging party — much like Benjen Stark — only, Brynden became the Three-Eyed Raven. Now, the Raven is dead, but Meera escaped the cave with Bran and (surprise) a sword.
In the latest episode, we see it in the scene where Benjen is speaking to Bran.
SmokeScreen came up with a theory that the sword might be Dark Sister itself. If it was in the cave, and the cave belonged to the Raven (who was actually Brynden Rivers — did you get it?), it may just be that we got a glimpse at Dark Sister after all. This might come well in handy since Meera will be protecting Bran against White Walkers.
That's all the Valyrian steel we've seen in the show, but let me know in the comments if you remember some other blade I left out!