Om Mani Padme Hum has always had special meaning to me. It was probably the first Buddhist mantra/chant I was introduced to, in the early 1970’s. We meditated to this mantra when I was in Kathmandu in 1976.
Om Mani Padme Hum is the mantra of Chenrezig, the embodiment of compassion.
This YouTube video is one of the most melodic and beautiful versions I have heard.
(If the YouTube video is not visible here, you can find it at http://www.youtube.com/watch?v=eygz-RJ3bR4.)
I do not use a mantra as part of my regular practice. Yet sometimes Om Mani Padme Hum will arise spontaneously in my mind, especially if my mind is extremely agitated. To me, there is a strong connection between compassion and patience, both of which I find essential in being with my mind.
Meditation and Life 