Magic Hair

Examples of Magic Hair include:

Anime and Manga

From Inuyasha, there was Yura of the Hair, who collected the stuff and then used it as Razor Floss.

Medusa, whose hair was snakes.
The Biblical Samson was granted supernatural strength by God in order to combat his enemies and perform heroic feats, with includes: wrestling and killing a lion with bare hands, slaying an entire Philistine army with only a jawbone of a donkey, etc. There was a catch though: he couldn't drink any kind of alcohol and he couldn't shave his hair - if would do that, he would lose his super strength. Unfortunately, he told this to his lover Delilah, who then proceeds to cut his hair and sells him to the Philistines soldiers, who stab out his eyes with their swords. After being blinded, Samson is brought to Gaza, imprisoned, and put to work grinding grain. Later, the Philistines leaders and common people gather in the temple of their god Dagon, for having delivered Samson into their hands. They summon Samson in order to ridicule him, but once inside the temple, Samson asks a guard one question: can he lean on the central pillars? Soon enough the gathered Philistines realized something - hair is known for growing back...

Rapunzel from Tangled, whose hair has magic healing powers and serves as a Fountain of Youth.

The Monkey King Sun Wukong from Journey to the West. Every strand of his hair had magical properties, able to transform into virtually any object he desired, ranging from weapons to animals to a full-body, perfect replica of himself.
Susan Sto Helit of Discworld has hair that rearranges its style of its own accord depending on Susan's mood. It's one of the special things she has due to her being Death's adoptive granddaughter.
In Warbreaker, the hallmark of the royal family of Idris is hair that changes color in reponse to the person's emotions (or voluntarily, with practice), and can also be grown out at will. It's hinted in the novel, and confirmed by Word of God, that this is a subconscious manifestation of the royal family's Voluntary Shapeshifting powers, and they might be able to take it further with practice.

Subverted in Bayonetta. It appears that the title character is using her hair to make giant fists, giant feet, and giant dragons, but reading Antonio Redgrave's notes reveals that witches need a medium in order to summon these things. In theory they could use anything, but hair is the most readily available. It's not that the hair is magic, more like magic things are happening to the hair.
Millia Rage from the Guilty Gear series. After losing her parents, she was adopted by a Assassin Syndicate, where she practiced in the art of Hi-Deigokutsuipou, or the "Six Forbidden Magics", with gave Millia's her ability to control the movement as well as alter length and shape of her hair at will.
Akiha Tohno's special ability in Tsukihime is draining heat (life) out of everything she touches with her hair in its red mode.

Monsterful has Lawrence Spectrum and his father Christopher Spectrum, both ghosts that possess a "flame-like" hairstyle that acts as an expansion of themselves. Christopher takes the power even further by being capable of generating entire illusions and manifestations with his flame.
- Samantha Thing is another example of this, her hybrid Monster species (half futakuchi-onna) gives her everlasting long hair and the ability to freely manipulate it.
El Goonish Shive has this. "So wait, officially, does hair spontaneously change color?" It's a side effect of other magic, though.

In the Animated Adaptation of I Dream of Jeannie, Jeannie used her ponytail as a Magic Wand, pointing it towards what she wanted to magic.
My Little Pony: The mane and tail hair of all the Little Ponies, due to the inherently magical nature of the ponies themselves. This is a plot point in the serial "The Glass Princess", in which Vain Sorceress Porcina has some of the ponies captured so that she can use their hair to mend her magic cloak.
Lady Lovely Locks: Her hair is so magical the Big Bad keeps plotting to get it. There's a reason the Brazilian title translates as "Princess of Magical Hairs".