I love the story of the Banshee. I can't remember her origins, but she always signaled someone's death by her wails and crying. It is said that the person destined to die never hear's her and is sparred the fright of it all. In other legends, it's said that there are many. In some depictions she is combing her hair because of her fair hair. 
From Wikipedia:
"In later versions the banshee might appear before the death and warn the family by wailing. [1] When several banshees appeared at once, it indicated the death of someone great or holy.[2] The tales sometimes recounted that the woman, though called a fairy, was a ghost, often of a specific murdered woman, or a woman who died in childbirth.[3] "
(Another legend I heard of was she announces the death of a child - she had lost her own children in a horrific way and thus arrived to take dying children, almost as though taking her own)
"Banshees are frequently described as dressed in white or grey, and often having long, fair hair which they brush with a silver comb, a detail scholar Patricia Lysaght attributes to confusion with local mermaid myths. This comb detail is also related to the centuries-old traditional romantic Irish story that, if you ever see a comb lying on the ground in Ireland, you must never pick it up, or the banshees (or mermaids — stories vary), having placed it there to lure unsuspecting humans, will spirit such gullible humans away. Other stories portray banshees as dressed in green, red or black with a grey cloak.
Another is the Coiste Bodhar (chost de bower) - The Death Coach. It is particularly strong in Irish culture, but can be found in others. The coiste bodhar warns of imminent death to either oneself or to a close relative. In Ireland in particular the Death Coach is seen as a signifier of the inevitability of death, as the belief goes once it has come to Earth it can never return empty. I don't know what would happen if it did return empty. The coach is driven by a headless coachman named Dullahan - cool, no?
Of course, there are the Leprechauns, also known as the Little People are immortals who love mischief. They were originally known to wear red, whereas trooping fairies wore green. They stad about 2 feet tall, and always dressed to impress in their dress coat, cocked hat, shoes and buckles. It is said if you were to catch a leprechaun, he would grant you three wishes, but no more. They are also quite devious and always looking for new tricks. One legend says if you take your eyes away from the Leprechaun, he will make a break for it. My trade, leprechauns are cobblers, or shoemakers, which is why you can always hear a tapping of a hammer if one is near.
A lesser known one is the Pooka (puca). It is a shape-shifter which can take on pleasant or terrifying forms. Usually seen as a horse, goat, rabbit, goblin or dog. No matter what form it takes, it always has dark fur. It's ost common form is a sleek black horse with golden eyes - spooky, no?
From Wikipedia:
If a human is enticed onto a púca's back, it has been known to give them a wild ride, though unlike a kelpie, which will take its rider and dive into the nearest stream or lake to drown and devour him/her, the púca will do its rider no real harm. The púca has the power of human speech, and has been known to give advice and lead people away from harm. Though the púca enjoys confusing and often terrifying humans, it is considered to be benevolent.
If you have ever seen Disney's Darby O'Gill and the Little People, you'll know what I'm talking about. I really wish I could find out more about the legends. I think it would be AMAZING to go to Ireland and find out for myself.
History of St. Patrick's Day
"Little is known of Patrick's early life, though it is known that he was born in Roman Britain in the fifth century, into a wealthy Romano-British family. His father and grandfather were deacons in the Church. At the age of sixteen, he was kidnapped by Irish raiders and taken captive to Ireland as a slave.[1] It is believed he was held somewhere on the west coast of Ireland, possibly Mayo, but the exact location is unknown. According to his Confession, he was told by God in a dream to flee from captivity to the coast, where he would board a ship and return to Britain. Upon returning, he quickly joined the Church in Auxerre in Gaul and studied to be a priest.
In 432, he again says that he was called back to Ireland, though as a bishop, to save the Irish, and indeed he was successful at this, focusing on converting royalty and aristocracy as well as the poor. Irish folklore tells that one of his teaching methods included using the shamrock to explain the Holy Trinity (the Father, the Son, and the Holy Spirit) to the Irish people. After nearly thirty years of teaching and spreading God's Word he died on 17 March 461, and was buried at Downpatrick, so tradition says. Although there were other more successful missions to Ireland from Rome, Patrick endured as the principal champion of Irish Christianity and is held in esteem in the Irish Church.
In 432, he again says that he was called back to Ireland, though as a bishop, to save the Irish, and indeed he was successful at this, focusing on converting royalty and aristocracy as well as the poor. Irish folklore tells that one of his teaching methods included using the shamrock to explain the Holy Trinity (the Father, the Son, and the Holy Spirit) to the Irish people. After nearly thirty years of teaching and spreading God's Word he died on 17 March 461, and was buried at Downpatrick, so tradition says. Although there were other more successful missions to Ireland from Rome, Patrick endured as the principal champion of Irish Christianity and is held in esteem in the Irish Church.
Wearing of green
"Originally, the colour associated with Saint Patrick was blue. However, over the years the colour green and its association with Saint Patrick's day grew.[2] Green ribbons and shamrocks were worn in celebration of St Patrick's Day as early as the 17th century.[3] He is said to have used the shamrock, a three-leaved plant, to explain the Holy Trinity to the pre-Christian Irish, and the wearing and display of shamrocks and shamrock-inspired designs have become a ubiquitous feature of the day.[4][5] Then in the 1798 rebellion in hopes of making a political statement Irish soldiers wore full green uniforms on 17 March in hopes of catching attention with their unusual fashion gimmick.[2] The phrase "the wearing of the green", meaning to wear a shamrock on one's clothing, derives from the song of the same name."
"Originally, the colour associated with Saint Patrick was blue. However, over the years the colour green and its association with Saint Patrick's day grew.[2] Green ribbons and shamrocks were worn in celebration of St Patrick's Day as early as the 17th century.[3] He is said to have used the shamrock, a three-leaved plant, to explain the Holy Trinity to the pre-Christian Irish, and the wearing and display of shamrocks and shamrock-inspired designs have become a ubiquitous feature of the day.[4][5] Then in the 1798 rebellion in hopes of making a political statement Irish soldiers wore full green uniforms on 17 March in hopes of catching attention with their unusual fashion gimmick.[2] The phrase "the wearing of the green", meaning to wear a shamrock on one's clothing, derives from the song of the same name."
