Passwords in Oracle of Ages

Labrynna Secret
Received From: Defeat Onox at the end of Oracle of Seasons.
Told To: Oracle of Ages Title Screen.
Purpose: Begin a linked game in Oracle of Ages.

Ring Secret
Received From: The Red Snake in Seasons.
Told To: The Red Snake in Ages.
Purpose: Transport Rings from one game to another.

Clockshop Secret
Received From: Received from the woman near the Ember Tree.
Told To: The man in a secret basement behind the Clock Shop (dig around).
Purpose: Get the Master Sword.

Smith Secret
Received From: Subrosian in Rolling Ridge.
Told To: Subrosian Smith in Seasons.
Purpose: Get the Mirror Shield.

Pirate Secret
Received From: Girl south of the Black Tower.
Told To: A skeleton in the Pirate House in Seasons. (You must have exactly 777 Ore Chunks.)
Purpose: Bomb Upgrade.

Deku Secret
Received From: Deku Salesman in the Woods in the past.
Told To: Deku west of Great Moblin's Keep.
Purpose: Seed Upgrade.

Ruul Secret
Received From: Woman in the Mayor's House.
Told To: Mayor Ruul in Horon City.
Purpose: Ring Box Upgrade.

Graveyard Secret
Received From: Ghost near Syrup's Hut.
Told To: Ghost in the Graveyard in Seasons.
Purpose: Heart Container.

Biggoron Secret
Received From: Goron in the Abandoned Cave in the past where the Great Moblin's Keep is.
Told To: The Biggoron.
Purpose: Biggoron Sword.

Subrosian Secret
Received From: Subrosian in the cave next to the Mystery Tree on Rolling Ridge.
Told To: Subrosian in the cave west of where you first entered Subrosia.
Purpose: Bombchus.

Diver Secret
Received From: Diver in Zora Village.
Told To: Diver in Sunken City.
Purpose: Swimming Ring.

Fairy Secret
Received From: Fairy near the Wing Ruins.
Told To: Fairy behind the Waterfall in the Temple of Seasons.
Purpose: Heart Ring L-1.

Hero's Secret
Received From: Defeat Ganon.
Told To: Oracle of Seasons Title Screen.
Purpose: Start a "Hero's Game", which is identical to the normal game, only starting with an extra heart.

~ Thanks to PinkMonkey.