Celtic Fairy Tales

First published in 1892, "Celtic Fairy Tales" is an anthology of Celtic folklore tales collected and edited by Joseph Jacobs and one of the best of the crop. 
"Celtic Fairy Tales" includes some great tales such as "Munachar and Manachar", the "Brewery of Eggshells", and "Fair, Brown and Trembling".
Jacobs also includes an extensive Notes and References section if you want to follow up on each tale.