I follow the path of Pictish Magick, and my religion and Magick are therefore not often entwined.
So, for the benefit of other students of the Northern Celtic Gods, here is the following list. Keep in mind, though, that the Gods varied from region to region, so this is simply my list from what I know about the Celts from my family's birthplace in the Western Highlands of Scotland, the Goidelic Celts.
The Goidelic Celts' territory included Ireland, the Isle of Man, and the western highlands of Scotland. In language, race, and tradition these form a homogenous block.
Abhean - Harper of the Tuatha Dé Danann
Aes Sidhe - 'The people of the hills', collective name for the old Irish gods who dwell in hills.
Aeval - The Fairy Queen of Munster. She held a midnight court to determine if husbands were satisfying their wives' sexual needs, or not, as the women charged.
Agrona - Goddess of strife and slaughter
Ai - A poet god, a member of the Tuatha Dé Danann
Aibell - Fairy goddess
Aimend - Sun-goddess
Aine - Goddess of love and fertility. Later regarded as a fairy queen in County Limerick.
Airmed - Goddess of the Tuatha Dé Danann
Anann - Mother goddess; overlaps with Danu. Worshiped as a goddess of plenty. In her dark aspect, she formed a Fate trinity with Badb and Macha.
Anu - Fertility goddess, venerated as the mother of the gods
Arianrhod - Moon goddess
Badb - Goddess of war. She often assumes the form of a raven or carrion-crow (her favorite disguise) and is then referred to as Badb Catha, meaning "battle raven". Not only did she take part in battles themselves, she also influenced their outcome by causing confusion among the warriors with her magic. The battle-field is often called 'land of Badb'. She forms part of a triad of war-goddesses with Macha (Nemain) and the Morrigan.
Balor - God of death and the king of the Fomorians, a race of giants. He was the son of Buarainech and the husband of Cethlenn. Balor had only one eye, which he kept closed because anything he looked at would die instantly.
Banba - Goddess who represents the spirit of Ireland. She is part of a trinity of goddesses, the daughters of Fiachna, together with Fodla and Eriu
Bebhionn - Underworld goddess and a patron of pleasure
Bile - God of light and healing. Patron of sheep and cattle, Bel's festival is Beltaine.
Boann - Goddess of bounty and fertility, whose totem is the sacred white cow
Bodb - Goddess of battle
Branwen - Goddess of love and beauty
Bres - God of fertility and agriculture
Brigid - A three-fold goddess. Known by many names, Brigid's three aspects are (1) Fire of Inspiration as patroness of poetry, (2) Fire of the Hearth, as patroness of healing and fertility, and (3) Fire of the Forge, as patroness of smith craft and martial arts. Other names for her are Breo Saighead, Brid, Brigid, Brigindo, Brigandu, Brigan, Brigantia, Brigantis, and Bride.
Bronach - Goddess of cliffs
Cailleach - Referred to as the "Mother of All" in parts of Scotland. Also known as Scotia, she is depicted as an old hag with the teeth of a wild bear and boar's tusks. She is believed to be a great sorceress. She is also known to have created the earth. Another name for her is Skadi
Canola - She is the inventor of the Irish harp
Carman - A destructive witch, she was the goddess of evil magic
Cernunnos - "The Horned One" is a Celtic god of fertility, life, animals, wealth, and the underworld. Cernunnos is depicted with the antlers of a stag, sometimes carries a purse filled with coin. The Horned God is born at the winter solstice, marries the goddess at Beltaine, and dies at the summer solstice. He alternates with the goddess of the moon in ruling over life and death, continuing the cycle of death, rebirth and reincarnation
Cessair - A great magician, she became the first queen of Ireland
Cethlion - The prophetess of the Fomorians
Cliodhna - Goddess of beauty. She later became a fairy queen in County Cork
Creidhne - God of metal working. One of the trio of craft-gods of the Tuatha Dé Danann, as ae Goibniu and Luchta
Cu Roi - Sorcerer who is able to transform himself into various guises
Curoi mac Daire - Sun-deity, believed to be a storm-bringing giant, armed with an ax
Cyhiraeth - Goddess of streams. Her shriek is said to foretell death
Dagda - God of the earth and treaties, and ruler over life and death. He is a master of magic, a fearsome warrior and a skilled artisan. The Dagda is portrayed as possessing both super- human strength and appetite. His attributes are a cauldron with an inexhaustible supply of food, a magical harp with which he summons the seasons, and an enormous club, with one end of which he could kill nine men, but with the other restore them to life. He also possesses two marvelous swine and ever-laden fruit trees. One of his epithets is Ollathir, which means "All-father".
Danu - Earth goddess, matriarch of the Tuatha Dé Danann
Dia Griene - Daughter of the sun
Dian Cecht - Great god of healing and the physician of the Tuatha Dé Danann
Dwyn - God of love
Edain - Goddess who is associated with horseback-riding
Eriu - The goddess-personification of Ireland
Etain - Sun goddess
Fand - Both a Faery queen and a minor sea goddess who makes her home both in the Otherworld and on the Islands of Man. With her sister, Liban, she is one of the twin goddesses of health and earthly pleasures. She is also known as "Pearl of Beauty".
Fodla - One of the three goddesses who ruled Ireland before the first Gaels, led by Amergin, came to the island. She was given the honor of naming Ireland.
Goibniu - A smith god, son of the goddess Danu. He manufactures swords that always strike true, and he possesses the mead of eternal life. He makes the arms for the Tuatha Dé Danann together with Creidhne and Luchtainel. As a brewmaster he is unsurpassed and his beer gives the drinker immortality
Gwenn Teir Bronn - Goddess of motherhood
Hooded Spirits - A triad of Celtic deities who are associated with healing and fertility
Lir - Sea god
Lugh - Lord of every skill. He and his nature goddess consort (Rosmerta) are worshiped during the 30 day Lughnassad midsummer feast in Ireland. Fertility magic during this festival ensures ripening of the crops and good harvest. He is called Lamfhada or 'of the long arm' in Gaelic because of his great spear and sling. His animal attributes are the raven and the lynx
Mabon - Hunter-god
Macha - One of three aspects of the Morrigan, goddess of war. Macha feeds on the heads of slain enemies
Mag Mell - Mag Mell ("plain of joy") is a paradise where the deceased live. In contrast with other realms of the dead, Mag Mell is described as an idyllic island, or as a wonderful place at the bottom of the ocean
Manannan mac Lir - God of the sea and fertility, who forecasts the weather
Maponos - God of youth
Midir - Ruler of Mag Mor, the underworld
Mog Ruith - God of the sun who rides through the sky in a shining bronze chariot, or who flies through the sky like a bird
Morrigan - Goddess of battle, strife, and fertility. Her name translates as either "Great Queen" or "Phantom Queen," and both epithets are entirely appropriate for her. The Morrigan appears as both a single goddess and a trio of goddesses. The other deities who form the trio are Badb ("Crow"), and either Macha (also connotes "Crow") or Nemain ("Frenzy"). The Morrigan frequently appears in the ornithological guise of a hooded crow
Nemetona - Goddess of sacred groves or shrines
Nuada - Chieftain-god of healing, the Sun, childbirth, youth, beauty, ocean, dogs, poetry, writing, sorcery, magic, weapons, and warfare. Similar to the Roman god Neptune, Nuada also has an invincible sword, one of four great treasures of the Tuatha Dé Danann, that he uses to cleave his enemies in half.
Oengus Mac Oc - The god of love, beauty and youth. He is known for his physical beauty and golden hair, and because his kisses become birds.
Ogma - God of eloquence and learning
Ogyruan - God of bards
Rhiannon - A version of the horse-goddess Epona and of sovereignty. She is mistress of the Singing Birds
Tailtiu - Earth-goddess
Tethra - King of the Fomorians, as well as the sea god and god of the Otherworld
Teutates - God of war, fertility, and wealth
Tir na n'Og - "The Land of the Young". Another name for Mag Mell
Tuatha Dé Danann - the Irish race of gods, founded by the goddess Danu. These gods, who originally lived on 'the islands in the west', perfected the use of magic. They traveled on a big cloud to the land that later would be called Ireland and settled there.