_Early Irish Myths and Sagas_ (1981) by Jeffrey Gantz is a good place to start.
T.F. O'Rahilly's _Early Irish History and Mythology_ (1946) is something that
you'll have to read eventually -- if you want to know first hand what the
later scholars are yowling about. Proinsias Mac Cana's _Celtic Mythology_
(rep.1983) [pace McCone] and Daithi O hOgain's _Myth, Legend & Romance:
and Encyclopedia of the Irish Folk Tradition_ are also good reference sources.
Are you looking for translations and collections of the myths or