Instead of pentacles and pentagrams, here below are a few Celtic Symbols you can use in your magic. (Of course if you want to use pentacles and/or pentagrams go right ahead!)
A three pronged knot which symbolizes the Celtic philosophy that everything has 3 distinct yet interlocked levels - physical, mental, and spiritual.
Rounded spiral with three arms radiating from a central point, typically understood as standing for land, sea and sky which composed the foundatino of Celtic cosmology. This is found on a number of Irish Megalithic and Neolithic sites, drawn unicursally (that is, in one continuous line), suggesting a cycle of rebirth or resurrection. The most notable one is on the inside of the Newgrange pasage tomb, on the entrance stone and on some of the curbstones surrounding the mound. The sun, dying and rising every day, is a natural symbol or rebirth, and the triple spiral gives an obvious connection between the solar symbolism and the nine months of human gestation.
**Note: The dots are not always at the top of the rays** Represents the three worlds and the sign of divinity called the awen; stands for truth, knowledge, and justice.
Celtic Tree of Life
The ancient Celts saw the Tree of Life as a symbol of balance in the universe. A tree, with roots deep in the earth and branches stretching toward the heavens; the solid trunk of the tree unifying them, both in harmonious balance. The cosmos was shown inthe branches and they are woven together shwoing that everything in the universe is connectted. The Tree was a central part of early Celtic spirituality. The most sacred tree of all was the Oak tree which represented the axis mundi, the center of the world. The Celtic name for Oak, daur, is the origin of the word door - the root of the oak was literally the doorway to the Otherworld, the realm of the Fairy.
The spiral is probably the oldest symbol of human spirituality. It has been found scratched into rocks millenia old, on every continent in the world. The double spiral found in neolithic Celtic stone art also follows the path of the sun, describing the movements of the heavenly body over the course of a solar year.