The 24 Masks of Termina

Deku Mask - The first mask that Link receives. On the first day, get the moon tear from the observatory. Bring the tear to the Deku Scrub near the clock tower. Propel yourself up to the ledge of the clock tower at 12:00 midnight on the 3rd day. Get your ocarina back from Skullkid, play the song of time and go back to the Happy Mask Dealer to get the mask.

Great Fairy's Mask - After attaining the Deku Mask, get the lost fairy at the Laundry Pool and bring it back to the Great Fairy in North Clock Town as normal Link. The fairy will give you this special mask.
Special Use: The Great Fairy's Mask is used to find the missing fairies in each of the four dungeons. When you put the mask on in a room where there are fairies, the hair will shimmer.

Kafei's Mask - At 10:00 AM on the 1st day, go to the Mayor's office in East Clock Town and enter the room on the right. After Gorman leaves, talk to the large woman and she will give you Kafei's Mask.
Special Use: Kafei's mask is simply used to show the innkeeper, Anju, that you are looking for Kafei.

Blast Mask - At exactly 12:00 AM of the 1st day, go to North Clock Town. A short cut-scene will occur with a thief stealing a bag from an old woman. Slash at the thief with your sword to retrieve the bag. The old woman will give you the Blast Mask in gratitude.
Special Use: The Blast Mask is basically a bomb that you wear. If you're ever out of bombs, use this mask to blow things up. WARNING: You will lose life when using this mask!

Bremen Mask - To get this mask, go to the Laundry Pool at night and talk to the guy playing the music box. Listen to him tell his tale and he'll give you the Bremen Mask.
Special Use: The Bremen Mask is used to get animals to follow you. Use this mask at the Cucco house at Romani Ranch to get the Bunny Hood.

Bunny Hood - On the Final day, go to Romani Ranch and head all the way straight until you reach the Cucco house. Go in and talk to the guy there. Put on the Bremen Mask and march around until all of the baby Cucco's are following you. Once they all follow you, they'll grow up instantly and the guy will give you the Bunny Hood.
Special Use: The Bunny Hood simply makes you run a lot faster. Very useful for impatient types like me ;)

Mask of Scents - After defeating the Woodfall Temple, hop over around the left side of Deku Palace and enter the shrine. Follow the Deku butler to the end of the shrine to receive the Mask of Scents.
Special Use: Use this mask to sniff out mushrooms to take to Koume (or is it Kotake?) and she'll make you a potion. The easiest mushroom to find is in Stock Pott Inn on the second floor. Sniff the shorts and bottle up the mushroom.

Kamaro's Mask - At 12:00 AM of the first day, go out the north exit of Clock Town. Follow the fence to the left until you start hearing a strange tune. If you look out at the big mushroom things, you'll see some guy dancing around. Hop over to him and play the Song of Healing. He'll then give you his mask!
Special Use: This mask will enable you to do Kamaro's dance. Use this mask to show the dancing sisters in West Clock Town the Kamaro Shuffle to earn a piece of heart.

Goron Mask - After you get the Lens of Truth, look through it as soon as you leave the cave where you got it. You should see a Goron's ghost floating about. Talk to it and follow it all the way to his grave. Play the Song of Healing for him and he'll leave you the Goron Mask.

Don Gero's Mask - Light all of the torches in Goron Village to get the chandelier spinning. Now Goron roll over the ramp, breaking each chandelier piece until a big chunk of meat falls out of one of them. Take the meat to the Goron that's hungry and stuck on a ledge at Mountain Village. After chowing down, he'll give you Don Gero's Mask.
Special Use: Use this mask to talk to the 5 frogs to unite them at the pond in Mountain Village to get a piece of heart.

Stone Mask - After you get Epona, get a red potion and bring it to Ikhana Valley. Right after you hop over the second big fence, go to the right and find a circle of rocks. Look through the Lens of Truth to find a soldier sitting there. Give him the red potion and he'll give you the Stone Mask.
Special Use: Using this mask will render you invisible to all minor enemies and the Gerudo Pirates.

Zora Mask - Go to Great Bay Coast and look to the left for a seagulls flying around in circles in the ocean. Go to that spot to find a Zora lying there half dead. Push him to shore and play the Song of Healing for him to receive the Zora Mask.

All-Night Mask - To get this mask, first save the old lady from the thief at 12 AM on the first day (as you did to receive the Blast Mask). After this, speed up time to the 3rd day. At 10:00 PM, go to the Curiosity Shop to buy the All-Night Mask for 500 rupees.
Special Use: Use this mask to listen to Grandma's stories at the Stock Pott Inn at around 6-7 AM of the 1st day. You'll get two pieces of heart out of the deal.

Keaton Mask - After receiving the letter of Anju, delivering it to the mailbox, getting the pendant from Kafei and delivering that to Anju, go to the Laundry Pool on the 3rd day at 1:00 PM. The guy inside will give you the Keaton Mask along with a top priority letter to Kafei's mother.
Special Use: Put this mask on and pick up one of the moving bushes. When all the bushes disappear, a Keaton fox will appear and give you a quiz. Win the quiz to get a piece of heart.

Postman's Hat - After getting the Keaton Mask and priority mail, bring the mail to the Postman at around 3:00 PM to deliver to Kafei's mother. Follow the Postman to the Latte Bar. After he delivers the letter, meet him outside and he'll give you the Postman's Hat.
Special Use: Use this mask to check the mailboxes. One of them contains a piece of heart.

Garo's Mask - Go to the Gorman Ranch (first left on Milk Road) during the day and beat them in a horse race. After losing, they'll give you Garo's Mask.
Special Use: Allows you to reach Ikhana Valley. It also allows you to find and fight the Garo's.

Romani's Mask - Go to Romani Ranch on the first day and protect the barn from the alien poes. After that, return to the barn and take the horse & carriage ride to Clock Town. Protect the wagon from the persuing thieves and you'll receive Romani's Mask (and maybe even a big 'ol hug!)
Special Use: Use this mask to get into the Latte Bar. It's your proof of membership!

Mask of Truth - Defeat all 30 spiders in the Gold Skulltula House in Woodfall Swamp to receive this prize.
Special Use: This mask allows you to speak to animals and the gossip stones. Use this mask at the dog races to find out which dog feels his best to win!

Captain's Hat - Defeat General Keeta at the Ikana Valley Graveyard to receive this mask.
Special Use: Use this mask to speak to the Stallkids. It also totally freaks out that Skull King guy at Ikana Palace.

Gibdo Mask - After filling the dried up well, sneak into the Music Box House in the center of Ikana Valley and go downstairs. Play the Song of Healing for the mummy to receive the Gibdo Mask.
Special Use: This mask allows you to speak to Gibdos (the mummys).

Circus Leader's Mask - Go to the Latte Bar on the 1st or 2nd day with the Romani Mask on at around 10:00 PM. Help the Zora do a sound check. Gorman will be so touched by the song, he'll give you his mask.
Special Use: Use this mask while riding the wagon to Clock Town. The pursuing thieves will follow, but they won't try to break the milk jars.

Couple's Mask - This one's the most difficult to get. On the first day at 1:45 PM, go to the Stock Pott Inn. After the Postman delivers Anju a letter, put on Kafei's Mask and she'll ask you to meet her at 11:30 PM. Go to the kitchen of the Stock Pott Inn at 11:30 (she'll show at around 12ish). Anju will then give you a letter. Go stuff it in the mailbox outside and get to the 2nd day. Wait at the Laundry Pool. At around 3:00 PM, the Postman will bring the letter to Kafei. Go inside the door back there and talk to Kafei when he gets up. He'll give you a pendant. Take the pendant to Anju and forward up to the Final Day. Go back to the Laundry Pool and into the back door at 1:00 PM to get the priority mail. Bring the priority mail to Kafei's mother at the Latte Bar at 6:00 PM. Leave town and ride Epona to Ikhana Valley. When you get to the river with the broken bridge and two octoroks, put on your Stone Mask and take a right. You should see the thief prancing about. A little further down is 2 rocks, behind which hides Kafei. Talk to him and wait for the thief to open the rock door. Go in and beat the thief's security system to retrieve the Sun Mask for Kafei. Go back to Stock Pott Inn and take the first door on the right upstairs. Wait until the final hour for Kafei to come in. Anju and Kafei will be reunited and they'll give you the Couple's Mask.
Special Use: Use this mask and talk to the Mayor. This will break up the big town meeting which will prompt the Mayor to give you a piece of heart.

Giant's Mask - You get this mask from the Eyegore in the room just before TwinMold.
Special Use: Use this mask for the fight with TwinMold. It will turn you into a giant!!

Fierce Deity's Mask - Collect every single mask in the game and go through all four dungeons in the moon. When it's all said and done, you'll have no masks left. Talk to the kid with Majora's Mask on and he'll give you this spectacular mask which makes beating this game oh so simple :)