The Gayatri Maha Mantra is very ancient Vedic Mantra and is considered to be the most powerful and potent of all Mantras. It reads as follows:

Om Bhurbhuvah Swaha
Tat Savitur Varenyam
Bhargo Devasya Dheemahi
Dhiyo Yona Prachodayat.

This is considered to be a prayer to the Sun God. Many powers are supposed to accrue to him who recites this Mantra everyday. Gayatri Devi is a personified form of this Mantra.