The first four provide an excellent introduction for the stories themselves, guides through the complexities of the characters and events, and a semi-scholarly treatment.
Gods and Fighting Men, Lady Gregory; Colin Smythe; 1904, 1976; ISBN: 0-901072-37-0 (well-told stories). Also her Cuchulain of Muirthemne by the same publisher. Both pbk. These may be easier to find than her Complete Irish Mythology.
A Treasury of Irish Myth, Legend and Folklore (comprising Fairy and Folk Tales of the Irish Peasantry, ed. WB Yeats; in one volume with Cuchulain of Muirthemne, Lady Gregory); Avenel Books, New York (dist. Crown Publishers, New York); ISBN: 0-517-48904-X
Ancient Irish Tales, ed. Tom Peete Cross and Clark Harris Slover; Barnes and Noble, New York; 1936, 1996; ISBN: 1-56619-889-5. Early translations.
The Cycles of the Kings, Myles Dillon; Four Courts Press, 1994; ISBN: 1-85182-178-3. This is an expansion of a section of his Early Irish Literature.
The Christian Druids — On the filid or Philosopher Poets of Ireland, John Minahane; Howth Free Press, Dublin, 2008; ISBN 978-0-955316-30-2. This is the long-awaited second edition of the out-of-print 1993 book.
A Dictionary of Irish Mythology, Peter Beresford Ellis; Oxford, 1987; ISBN: 0-19-282871-1. Complementary to Smyth's Guide (above)
Old Celtic Romances, PW Joyce; 1879; reprinted recently by Roberts Wholesale Books, Dublin; no ISBN. A bit quaint, but good retellings. All Irish stories, in spite of the title.
Fionn mac Cumhaill: Celtic Myth in English Literature, James MacKillop; Syracuse University Press, 1986, 2001. Fionn in Irish literature, the myth of Fionn, Macpherson's Ossian, Fionn in modern literature, Finnegans Wake.
On Raven's Wing (US title The Red Branch), Morgan Llewelyn; Mandarin; 1990. This is a well-told fictionalised version of the Táin with a strong psychoanalytical slant on Cúchulainn.
Take the Kids -- Ireland, Amy Corzine, Cadogan, 2004 ISBN 1-86011-110-6. This tourist guide is unusual for two reasons: the writing is sparkling and genuinely enthusiastic, and the author has included a large number of myths, legends and historical and folk tales.
Shapeshifter, Holly Bennett, Orca, 2010 ISBN 9781554691586. This character-driven Young Adult novel is based on the traditional legend of Sive, the mother of Oisín enchanted by an evil wizard. The strongly affecting ending builds upon a brief and vague mention in medieval literature of Sive's and Oisín's fates and resolves the mystery in a highly satisfactory and imaginative style.
Irish, Welsh and General Celtic Interest
Celtic Heritage, Alwyn Rees and Brinley Rees; Thames and Hudson, 1961; ISBN: 0-500-27039-2. An unsurpassed comparative look at Irish and Welsh traditional literature.
Dictionary of Celtic Mythology, James MacKillop; Oxford University Press, 1998; pbk 2000 ISBN: 0-19-280120-1. By the author of Fionn mac Cumhaill above. One of the most widely recommended reference books on the subject, and especially good on Irish material.
Myths and Legends of the Celts, James MacKillop; Penguin, 2005; ISBN: 0-140-51552-6. An expanded narrative version of the Dictionary that takes in the latest historical and archaeological evidence and scholarly opinion. As with the Dictionary, Irish material predominates.
Celtic (Myths and Legends Series), TW Rolleston; Bracken Books, London, 1912, 1985; ISBN: 0-946495-84-X. This is one of the many books surpassed by Rees and Rees, but very readable.
Mythology of the Celtic People, Charles Squire, Senate, 1998; ISBN: 0-09-185043-6. This is a reprint of Celtic Myth and Legend: Poetry and Romance, Gresham, 1912. A bit old-fashioned, but readable.
The Celtic Reader, ed John Matthews; Aquarian/Thorsons, 1992; ISBN: 1-85538-228-8. Matthews has dusted off obscure classics and made them available to modern readers. Worth buying for one piece alone -- a short story by the Irish mystic George Russell (Æ), "A Dream of Angus Oge", in which Angus shows a young boy how the rising sun at Midwinter fills his caisleán (Newgrange) with golden light. The story was published in 1915. It was 60 years later that the event was physically seen for the first time in some 4000 years.
Gods and Heroes of the Celts, Marie-Louise Sjoestedt; Four Courts Press, 1994 (Methuen, 1949); ISBN: 1-85182-179-1. This is Myles Dillon's translation of Sjoestedt's 1940 Dieux et Héros des Celtes. A psychoanalytical approach.
The Celts, Nora Chadwick; Penguin, 1970 (no ISBN). One of the standard basic books on the Celts.