Subhanahu wa ta'ala : This is an expression that Muslims use whenever the name of Allah is pronounced or written. The meaning of this expression is: "Allah is pure of having partners and He is exalted from having a son."
Muslims believe that Allah is the only God, the Creator of the Universe. He does not have partners or children. Sometimes Muslims use other expressions when the name of Allah is written or pronounced. Some of which are: "'Azza Wa Jall": He is the Mighty and the Majestic; "Jalla Jalaluh": He is the exalted Majestic.
src : http://www.usc.edu/
Subhanahu wa-ta'ala (Arabic: سبحانه وتعالى) is an Islamic Arabic phrase meaning, "glorious and exalted is He (Allah)." The phrase (often abbreviated to "swt") appears after the name of Allah in Islamic texts such as the Qur'an and the Hadith. Saying this phrase is seen as an act of reverence and devotion towards Allah among Muslims.
src : http://en.wikipedia.org/wiki/Subhanahu_wa_ta'ala