Namah Shivai (नम: शिवाय) is the most sacred and powerful mantra to please Lord Shiva. The Five letter mantra (containing Na, Ma, Shi, Va, Ya ) has great effect on the body and the soul which is discussed in the article Aum Namah Shivaya.

Shiva Panchakshar Stottram is one of the beautiful stottram glorifying Lord Shiva and the the five letter maha-mantra (Na-Mah-Shi-Va-Ya).