I chose two different ones. The first and lesser one is the Egyptian deity Thoth. He is one of my favorite symbols of all time, and I keep a statue of him in a location where it can almost always be seen. He represents and awful lot to me that touches on the most basic aspects of my personal path; knowledge, balance, plus writing and the sciences.
More important to me is the Septagram (also and commonly called the Heptagram). This holds many, many meanings for me. First of all, it is a symbol for the seven planets of ancient alchemy, representing a universe in balance (balance in general) as well as the great work, the symbolic transmutation of the Self from lead into gold. Next, it represents the great mother, the feminine energy of the universe (symbolic for me), plus Babalon and the City of the Pyramids in my interpretation of Thelemic beliefs. Following that, it represents balance and therefore Self-mastery, Self-perfection, etc. On top of that, it represents the 7th sphere of the Tree of Life in Jewish mysticism (touching on my birth religion) which stands for victory and eternity. Finally, it represents completion. I wear one around my neck almost every waking hour as well have one on my wall and will soon have a tattoo of one.