These are the overtly pagan designs I've found - pagan including Wiccan and many other paths. The fact that I've listed a site here does not constitute an endorsement of the designs on it. Some of them are, by my standards, downright ugly. Others just aren't to my tastes - but they are pagan. If you know of a site I've missed, please let me know!
Avalon Stitchery, "Pagan/Celtic/Medieval Cross-Stitch Patterns Designs by Margaret March." Margaret is just getting started but has two very nice free patterns available and plans to release more soon.
MagickStitches is a mailing list described as: "For Pagans, Wiccans, or any Earth Traditions interested in sharing techniques and discussion related to needlecrafts as a magickal tool. All needlecrafts are welcome-embroidery, counted cross stitch, quilting, needlepoint, crochet, and more. Discussion may focus on specific projects (ex: Tarot bag or altar cloth), project ideas or seasonal items."
Crafting the Craft is a mailing list that puts out one free project a month. They aren't all needlework, but some are, and all the old projects are available in the list archies. They've just announced a new list as well, Paganettes, for kid-oriented projects.
Cutworks has some Green Man designs as well as some lovely Egyptian patterns.
Witches Stitches has lovely designs - I have their Elemental Cosmos pentacle in my "to do" stash. They've recently added a free Winter Solstice design, as well. If you're in Atlanta, Phoenix & Dragon Books carries some of the WS designs in their store.
Crafts from Pan is the first site that you will find any time you do a web search for pagan or Wiccan designs. There are several Celtic designs there as well.
Original Magick Designs has graphs for the Rider-Waite tarot desk as well as a Wiccan Rede sampler with a knotwork border.
Sacred Spiral has some generic pagan designs that aren't specifically for cross stitch but could be used for it with little effort.