Zaishen Medallion

The Zaishen Medallion is a collectable item you recieve when you win in PvP during the Guild Wars Nightfall PvP Preview Event. It is not confirmed if this is a permanent addition or just for the weekend. You take the Medallion to the Zaishen Supply Master in the Great Temple of Balthazar. If you collect 30 Medallions, you can exchange them for either Crème Brûlée or a Flask of Firewater. If you collect 50 Medallions, you can exchange them for a Flame of Balthazar. If you collect 10 Flames of Balthazar, you can exchange those for a Celestial Sigil. That is 500 Medallions needed to get the sigil.

Random Arena and Team Arena
You receive 5 Medallions for winning, an additional Medallion for a flawless victory, and 5 additional Medallions for each 5 consecutive wins.

Heroes' Ascent
It is not yet known how many Medallions are awarded for winning, flawless victories, nor consecutive wins.

Guild versus Guild
It is not yet known how many Medallions are awarded for winning normally, but Flawless Victory rewards you 25 Medallions. (So I'd assume 20 for a normal victory)