Sword Quests
There are a few upgrades you can get for your main weapon. Below is a quick list of how to get them. These are also found throughout the Walkthrough.

Razor Sword
 - Bring 100 Rupees to the Mountain Smithy in Mountain Village. You must melt the furnace by using a Fire Arrow, Hot Spring Water, or killing Goht (making it spring).
 - If you pay them 100 Rupees, they'll sharpen your sword, making it do twice as much damage. It only lasts for 100 strikes though...

Upgrade: Razor Sword

 - By far, the coolest looking of all the swords in this game. This bad daddy does twice the damage of your Kokiri Sword!
 - Unfortunately, it's only as good as the money you put into it, and after 100 sword slashes, it will revert back back to its old form. =(

Gilded Sword
 - There's a few steps to get this. It's easier done after you've already completed the Snowhead Temple and saved.
 * Beat Goht (Snowhead Temple Boss) on the First Day or Night.
 * Win at the Goron Races (Gold Dust) also on the First Day or Night.
 * Forge your Kokiri Sword into the Razor Sword (Need 100 Rupees).
 * Forge your Razor Sword into the Gilded Sword (Need Gold Dust).

Upgrade: Gilded Sword

 - Your Kokiri Sword will now do twice as much damage, and never dull!
 - This is the second best Sword in the game, and it's most certainly worth the trouble you went through to get it.

Great Fairy Sword
 - The Great Fairy Sword is actually the reward for collecting all of the Stray Fairies in the Stone Tower Temple. See the Stray Fairies or Walkthrough sections for more information.

New Item: Great Fairy Sword

 - The strongest sword in the game. Does four times as much damage as the sword you start with. Unfortunately, it's an item, meaning you have to use it with a (C) button. That  and it has an awkward swing angle... All well...