The Celtic Pantheon is old, deeply rooted in nature, and focuses on every person's resourcefulness and work ethic.  There are no lay-abouts with this group of cutters.  As a planar pantheon, they are relatively young, but very popular with planewalkers.  Why?  Most of them are based in Tir na Og in the outlands, and therefore their priests lose no spellcasting levels around the great wheel.  They also found in many Dungeons & Dragons suppliments.  As for resources, I used (in order of age): (1) Legends & Lore by James M. Ward and Troy Denning [pgs. 57 - 69], (2) On Hallowed Ground by Colin McComb [pgs. 66 - 75], (3) Dragon Magazine #283, "Do-It-Yourself Dieties" by Stephen Kenson [pg. 35], and Forgotten Realms Campaign Setting by Greenwood, et al [pgs. 234-251].  All these works help me create this pantheon guide for those interested in playing Celts.  All the gods below are in the following form:
 

Diety	Power Level	Diety Alignment	Worshipper Alignment
Portfolio	Symbol	Typical Worshippers
Domains		Favored Weapon(s)

In all of the forms, one domain will be in bold.  To keep the flavor of the diety, it is highly recommended that clerics of that diety chooses that as one of his domains.