The Shurangama Mantra (http://en.wikipedia.org/wiki/Shurangama_Mantra) is the longest in the Buddhist canon. It contains 5 major Sections and 554 lines of Siddham Sanskrit. It is considered to be the king of mantras because it is the longest and most important.
It bestows numerous Dharmas, including :
- Dharma of Accomplishment : that means by reciting the Shurangama Mantra, whatever method you are practicing will be perfected; whatever thing you want to do will get done.
- Dharma of Increasing Benefits : that means, for example, if you don't have enough resolve for the Way in your practice, by reciting the mantra you can increase your wisdom; increase your Bodhi mind; increase the power of your vows; everything will get better. When you recite the mantra, everything you hope increases will surely do so! It will increase for others, too.
- Dharma of Quelling Disasters : that means that if a calamity is due, reciting the mantra will make it disappear.
(source : The Shurangama Mantra, The Efficacious Language of Heaven and Earth / http://online.sfsu.edu/~rone/Buddhism/Shurangama/Shurangama%20Mantr...)
Learning tools, including audio files and PDF version of the mantra, are available on this page :