I myself am rather partial to the followng two religious symbols:
Number One: The Celtic High Cross

It takes the Crucifix, and blends it with the Celtic Knot artistry, to create possibly a rather intricate and beautiful-looking symbol which I'd actually wear on a necklace.
Number Two: The Yin-Yang.

A prominent Taoism symbol, symbolising balance and harmony. It also has the advantage of looking extremely awesome, I don't know what it is about the Yin-Yang, but it's among the best looking symbols (of anything) in the world, in my opinion.