YL= Only usable as Young Link
AL= Only usable as Adult Link
BL= Take a wild guess :)

Swords:

Kokiri Sword (YL)
Found: In the Kokiri Training Center, on the southern area of the Kokiri Forest.
About: Your worst sword. However, it's the only sword usable as a child, so you're stuck with it for then. At least most of the enemies are too weak to withstand more than a few shots.

Master Sword (AL)
Found: In the Temple of Time after beating the Jabu-Jabu's Belly dungeon.
About: Probably the games most well-rounded sword. Twice as powerful as the Kokiri Sword, and a great Z-Targeting swordfighting weapon.

Biggoron's Sword (AL)
Found: Obtained from Medigoron atop Death Mountain, as the last step of the Biggoron's Sword trading sequence.
About: IMO, the games best weapon. Twice as powerful as the Master Sword, and most enemies go down after just one shot. The one and only downside to this weapon is that it takes two hands to use, therefore your shield can't be used while the sword is out of its sheath.

Boots:

Kokiri Boots (BL)
Found: You start the game off with these things.
Use: Standard boots, nothing special. Good speed, good traction, but nothing else.

Iron Boots (AL)
Found: In the Ice Cavern behind Zora's Fountain.
Use: These boots are great for sinking. Step into the water with these on, and you can examine the bottom. Of course, on land they slow you down quite a bit.

Hover Boots (AL)
Found: In the beginning of the Shadow Temple.
Use: These are pretty damn cool. You can hover above water or thin air for short periods of time. If you want to move faster on land, use the forward roll continuously with these on.

Tunics:

Kokiri Tunic
Found: Standard tunic that you start the game off with. Well, you don't think he started naked, now do you?
Use: It's good for...nothing. Really, except maybe to avoid freezing to death or being laughed at.

Goron Tunic
Found: You get this Tunic by stopping the tiny, rolling Goron in Goron City as an adult, using a bomb. Talk to him for a while, and eventually he gives it up. Also available at the Goron City shop for 200 rupees.
Use: It's a good, heat-resistant tunic, and necessary unless you are extremly fast (like me).

Zora Tunic
Found: You get this, the last tunic, by unfreezing King Zora as an adult. Also can be bought at the Zora's Domain shop for 200 rupees.
Use: This is only good if you're real slow, since you never need to be underwater for over a minute.

Shields:

Deku Shield (YL)
Found: This is purchased for 40 rupees at the Kokiri Forest shop. These can be found anywhere really, as Business Scrubs sell them in certain dungeons.
About: Standard defense for Yound Link. If you touch fire while this is equipped, it burns, and you have to purchase/find a new one.

Hylian Shield (BL)
Found: Purchased at Hyrule Market for either 80 rupees, or you can talk to the Death Mountain Trail Guard and get it at a reduced price. OR, you can go into Kakariko Graveyard, and search inside the graves for it.
About: As Young Link, you hold it over your head. Good for falling boulders. As an adult, you use it properly, and can Z-Fight with it. Wear Zora Tunic with it, it looks cool.

Mirror Shield (AL)
Found: Found in the Spirit Temple as an adult, after killing the second Ironknuckle.
About: This is the games strongest shield, which is it's upside as well as its downside. You cannot deflect Deku Nuts back anymore, they will shatter when hitting your shield. Tough. Also, deflects light and Koume and Kotake's energy blasts. Looks great with the Goron Tunic.

Arrows (All AL):

Normal Arrow
Found: The first arrows, along with the Bow to shoot them with, are found in the Forest Temple.
Use: Duh, it fires a standard, untouched arrow. Can be turned into a fire arrow if shot through a torch.

Fire Arrow
Found: In Lake Hylia. Warp there (or don't), and read the plaque near the Triforce symbol. Come daybreak, shoot the sun. You should then see what to do.
Use: This sets your arrows on fire before they hit your enemy. Costs 2MP. Does double damage as far as I can tell. Also, it melts white ice.

Ice Arrow
Found: This is the big treasure of the Gerudo training center. Worth it? Maybe.
Use: This makes your arrows very icy. This also costs 2MP, but it's worth it. Some enemies will shatter into many pieces if you hit them after freezing them.

Light Arrow
Found: Given to you after beating the 5th Temple, whether it be the Shadow or Spirit. Ouchies! 4MP to use just one of these ultra-powerful arrows.
Use: Necessary to beat Ganon's Tower (used on him and those weird thingies in the barriers).

Silver n' Gold

Silver Scale (BL)
Found: This is gotten by winning the Diving Game {See Mini-Games} at Zora's Domain. Necessary to beat the game.
Use: It allows you to dive for up to 5 seconds.

Golden Scale (BL)
Found: You can get this by catching a large fish as an adult.
Use: It allows you to dive for a seven count. Man, Link sucks at diving. Anyways, try it in the Lakeside Lab as an adult, hehe.

Silver Gauntlets (AL)
Found: At the end of the children's version of the Spirit Temple, after beating Ironknuckle. Only can be used as an adult, however.
Use: By now, you've run into one of those stupid blocks that says something about silver hands, right? Well, you can move them if you're wearing Silver Gauntlets.

Golden Gauntlets (AL)
Found: In the Shadow Barrier of Ganon's Castle. Unlike the Golden Scale, you DO need this to beat the game.
Use: Allows you to lift and HURL objects so heavy it's ridiculous!

C Items:

Hookshot/Longshot (AL)
Found: Retrieved by racing Dampe in the Kakariko Village graveyard as an adult. The upgrade to Longshot is found in the Water Temple after killing Dark Link.
Use: This sticks to wooden things and targets, and pulls you to them. Great, since it works on treasure chests.

Megaton Hammer (AL)
Found: In the Fire Temple, on the 5th floor (the top floor). this mythical Hammer has the power to crush some rocks. Use it on the Gossip Stones for laughs. Necessary to activate rusty switches and to kill Volvagia.

Bombs (BL)
Found: Anywhere really. Can be bought at shops, found under grass, or purchased from some Business Scrubs.
Use: Obviously, you use them, and they blow up, wiping out any enemies and bombable walls nearby. If you swing your sword at a wall, a bombable section sounds different than the others. It also looks different in most cases.

Deku Nuts (YL)
Found: Anywhere really. Can be bought at shops, found under grass, or purchased from some Business Scrubs.
Use: Used as a weapon, and only that. Ineffective on most creatures, but wreak havoc in Jabu-Jabu's belly. You can also use it to freeze certain enemies if you want. Whatever.

Deku Sticks (YL)
Found: Anywhere really. Can be bought at shops, found under grass, or purchased from some Business Scrubs.
Use: Great device for lighting torches. Can also be used as a formidable weapon, but snaps too easily. Burns out if on fire too long, so be careful.

Bottle (BL)
Found: There are four bottles:
1. Win Talon's Super Cucco-Finding Game at Lon Lon Ranch. As a child of course. Talon isn't there as an adult, you moron.
2. Catch all the chickens in Kakariko Village and return them to their pen. The Chicken Lady there will give you a bottle.
3. NECESSARY: As a kid, in Lake Hylia. Next to the entrance to Zora's Domain, way at the bottom. Has a letter inside.
4. As an adult, find all 10 Super Poes in Hyrule Field and sell each one to the Poe Man in Hyrule Market. Strange guy.

Use: Used for two purposes. One is to catch and carry things, such as bugs, fish, potions, etc. Another is versus Ganondorf or his Phantom, use it to deflect the energy bursts back at him.

Bombchus (BL)
Found: In a chest in the Spirit Temple, and one in Ganon's Castle. Also can be bought for 200 rupees from a man in the Haunted Wasteland or at a hidden shop in Hyrule Market at night. Also, your Gold Skulltula prize for 40 tokens.
Use: A cool, necessary weapon. Great for squaring off against Ironknuckle in case you're low on life or just plain suck.

Magic Beans (YL)
Found: Bought from the fat boy in Zora's River. Starts at 10 rupees, then 20, then 30, etc. until you reach 100.
Use: As a kid, go find a soft soil spot, and plant a bean in there. As an adult, come back and lookie there, a platform that you can ride. Crucial in getting a few Golden Skulltulas.

Bottled Bugs (YL)
Found: You can either buy these at a potion shop, or catch them. They're usually under rocks.
Use: Plant them in a soft soil spot, and a Golden Skulltula will soon pop out. Remember, 3 bugs come out, and you can recatch one, and he'll turn into 3. Repeat as needed.

Lens Of Truth (BL)
Found: In the tricky Kakariko Village Well, after you beat Dead Hand.
Use: Used to "See the truth" Really, you just use it to see invisible things and fake things.

Fairy Ocarina (YL)
Found: Given to you by Saria once you have the Kokiri Emerald and try to leave the forest.
Use: This Ocarina is used to play the first couple of songs for the beginning, but it disappears once you retrieve the.....

Ocarina Of Time (BL)
Found: Thrown in the moat by Zelda after you've collected all 3 Spiritual Stones and returned to Hyrule Market.
Use: Comes with 1 free tune, the Song Of Time, which is used to open up the secret door in the Temple of Time. Also plays the other 12 songs.

Masks
(Bunny Hood, Spooky, Keaton, Skull, Gerudo, Zora, Goron) (YL) Found: In the Happy Mask Shop as a child. The first four masks must be sold, and they access the other three and.....

Mask Of Truth (YL)
Found: After you've sold the other four masks, return to the Happy Mask Shop and find it there.
Use: Like the other masks, you can use it to talk to other people and get odd responses. Also, you can use it to talk to the Gossip Stones (1-eyed statues).

Weird Egg (BL)
Found: Given to you as a child by Malon, outside Hyrule Castle
Use: As a kid, when hatched it is used to wake Talon at Hyrule Castle.

Pocket Egg
Found: Given to you by the Cucco Lady in Kakariko Village
Use: Is the first step in the Adult Link trading Sequence. Used to awaken Talon in the house in Kakariko