Non-Hellenic and general pagan
Ludmila Zeman: Gilgamesh the King, The Revenge of Ishtar and The Last Quest of Gilgamesh
I can’t say enough about these books – they’re just amazing. Ms. Zeman did extensive research into ancient Babylonian art; when she sent a draft of the first volume to the British Museum to have it checked for accuracy, they ordered 1,000 copies to sell in their gift shop!
Kathy Henderson: Lugalbanda: the boy who got caught up in a war
This is (I believe) the oldest complete story in the world, even older than Gilgamesh (some scholars think Lugalbanda may have been the father of Gilgamesh, although I don’t know if this is clear). Nicely retold and illustrated.
Leo Lionni: Frederick
A sweet, simple, old-fashioned children’s classic – and a fine example of what being a Bard is all about.
Dennis Haseley, ill. Michael Hays: My Father Doesn’t Know About the Woods and Me
Sadly, out of print. This is a truly amazing book. On the surface, it seems to be just a story about an imaginative boy walking with his father in the woods, pretending to be various animals; but read it once, and be convinced that something much older and deeper is happening. Every time I read it, I hear echoes of the Song of Amergin.
Gail E. Haley: The Green Man
An interesting medieval-tinged tale of the Green Man, by the Caldecott award-winning author of A Story, A Story. Out of print. If you can get it, I recommend the hardcover edition because of the fantastic end-papers.
Bel Mooney: The Green Man
Another Green Man story; this modern-day tale is from the UK (and at 15 pounds, a heck of a lot cheaper than trying to buy it in America, even with trans-Atlantic shipping). I like the way it depicts the slow dawning of nature awareness and the level of subtle detail in the illustrations.
Audrey Wood, ill. Ned Bettinger: When the Root Children Wake Up
The illustrations in this retelling of Sibylle von Olfers’ classic nature story are just breathtaking; miles ahead of the ‘twee’ fairies in the original. A fun nature-awareness story for the very young that begs to be read aloud.
Douglas Wood, ill. P. J. Lynch: Grandad’s Prayers of the Earth
I can’t tell you how much I love this book; it will break your heart and then put it right back together again, with Gaea inside.
And, finally…
Helen Berger: Grandfather Twilight
Happy sigh.
ADDENDUM: and one item that is not actually a book, although there are books related to it… the “Maurice Sendak’s Little Bear” cartoon series that ran on Nick Jr. in the late 1990s (and still runs on Noggin) is *exceedingly* pagan-friendly, especially to those of the druid/earth-centered variety – I’m sure that I could put together a list of episodes for the whole Wheel of the Year (I can name off good episodes for Winter Solstice, Imbolc, Lughnasadh and Samhain without even stopping to think about it!).
The series is based, of course, on the classic children’s books written by Else Holmelund Minarik and illustrated by Maurice Sendak – Sendak was an executive producer, and IIRC Ms. Minarik even wrote an episode or two herself. The series goes beyond the books, though, IMO; and it’s done in such a sweet and old-fashioned style that I enjoy them as much as my daughter does. I love it also because it teaches moral lessons *by example*, just showing the characters living their lives; you don’t have an episode *about* kindness, or *about* cheating, like so many kid shows do – the characters just *are*.
Executive Pagan 
The Gilgamesh books are indeed fabulous. We bought them for our little boy when he was born… of course, hos middle name is Gilgamesh, so it just made sense.