Hey guys, here's most of the books (and even one site) that I thoroughly recommend to "Celtic" Pagans (this list was typed from memory, off the top'a my head, so some spellings and itles may be off):

* A History of Pagan Europe", by Prudence Jones and Nigel Pennick
* "European Paganism", by Ken Dowden
* "The Pagan Religions of the Ancient British isles", by ROnald Hutton: Don't take this book very seriously, because it is HIGHLY flawed due to a flawed methodology and unacknowledged BIAS of the highest degree that get's in the way of what MAY have actually happened. In fact, there's so much wrong with his books, as a whole, that I could write an entire article about the problems in his material that is accepted, sadly, as "definative" by the corpus of contemporary Pagans! <sigh>
* "The Stations of the Sun", by Ronald Hutton: Ditto!!!!!!!!!
* "The Gods of the Celts", by Miranda Green
* " The Quest for the Shaman", by Miranda Green
* "The Concept of the Goddess", ed. by Miranda Green
* The Great Queens", by Rosalind Clark
* "Celtic Goddesses", by Miranda Green
* "Dictionary of Celtic Mythology", by Miranda Green
* "Oxford Dictionary of Celtic Mythology", by James Mackillop
* "Celtic Mythology", by Proinsias Mac Cana
* "The Ancient Celts", by Barry Cunnlife
* "Pagan Celtic Ireland", by Barry Rafterie
* "Pagan Celtic Britain", by Anna Rosse
* "The Witch Figure", ed. by Venetia Newall
* "The Lore of Ireland", by Dathi O hOgain
* "Early Irish Myths and Saga", trans. by Jeffrey Gantz
* "The Tain", trans. and comp. by Thomas Kinsella
* "The Sacred Isle", by Dathi O hOgain
* "The Lady with the Mead Cup" (This is still a book on my "To Buy" List!!!)
* "Christianity: The Origins of a Pagan eligion", by Philipe Walter
* "The Celts", by John Collis
* "Celtic Heritage", by the Rees bros.
* "The Encyclopedia of Celtic Myth and Legend: A Source Book", by John & Caitlin Matthews
* "The Celtic Heroic Age", trans. and comp. by John Carey & John T. Koch
* "Cattle Lords and Clansmen", by Nerrys Patterson
* "Carmina Gadelica", by Alexander Carmichael
* "The Gaelic Otherworld: John Gregorson Campbell's 'Superstitions of the Highlands and Islands of Scotland' and 'Witchcraft and Second Sight in the Highlands and Islands'", ed. (with commentary) by Ronald Black
* "In Search of the Indo-European", by James P. Mallory
* Whence the Goddess: A Sourcebook", by Miriam RObbins Dexter
* "Indo-European Poetry & Myth", by M.L. West
* "The Oxford Introduction to Proto-Indo-European and the Proto-Indo-European World", by JP Mallory and DQ Adams
* "Inside the Neolithic Mind", by David Lewis-Williams
* "The Gods and Goddesses of Old Europe: Myths and Cult Images", by Marija Gimbutas
* "The Living Goddesses", by Marija Gimbutas
* "The Druids", by Stuart Piggot

These are all that I can think of, right now... What else would YOU add in an academic vein?