Angharad is utterly gorgeous. I adore it. I'd suggest it more often, but pronunciation is usually an issue.
Eirlys is another favorite and
Muirne is nice, although I prefer
Muirgheal /
Muriel. I'm not big on
Etain and
Morrigan, but I have nothing against them either.
Rather than listing my other favorites, why not go to the home page and look up names under "Irish names" or "Cornish / Manx / Scottish / Breton / etc. names." If they aren't listed on the home page, simply click on the link for "more names" and have fun. There's even a category for Celtic mythology, if I'm not mistaken.