Bookend:
Well, my immediate response is that you should check out The Golden Bough by James Frazer--it's one of the earliest and most influential works on comparative mythology and anthropology. Your university library has it. It's heavily focused on Goddess worship, magic, and the Year King ritual, all of which sound perfect for your needs.
The White Goddess by Robert Graves may also be useful to you. It discusses the archetypal Goddess that was likely the precursor to later European goddesses. Your university library has this one.
The other great work on comparative mythology is Joseph Campbell's The Hero with a Thousand Faces, but it is focused more on the hero than the gods. It is the original source of the word "monomyth." It's also available at your university library.
A couple others I found in your catalog that look promising (Call numbers are in parentheses):
The goddess and the warrior : the naked goddess and mistress of animals in early Greek religion, by Marinatos, Nanno (BL795.G63 M37 2000)
The rotting goddess : the origin of the witch in classical antiquity's demonization of fertility religion, by Rabinowitz, Jacob (BL820.H43 R33 1998)
The myth of the goddess : the evolution of an image, Baring, Anne (BL473.5 .B37 1991)
The goddess : mythological images of the feminine, by Downing, Christine, 1931- (BL785 .D66)
Gawain : Knight of the goddess : restoring an archetype, Matthews, John, 1948- (DA152.5A7 M3 1990)
Also
http://pantheon.org/ is always a good place for research on mythology.