Om

Tayata Om Bekandze,
Bekandze Maha Bekandze,
Randze Samu Gate Soha.

[url]http://www.youtube.com/watch?v=7IoG2UaevRo&feature=related[/url]

This mantra has great power in the elimination of pain, not just the symptoms but elimination of the root causes as well.

Bekandze is Tibetan pronounciation of Bhaisaijya, the name of The Medicine Buddha, Lapis Lazuli.

Om Tare Tuttare, Ture Mama Ayur,
Punye Jana Pushtim Kuru Svaha

is the White Tara mantra, with similar purpose and effect of the Medicine Buddha Mantra, especially for long-life however.