Below is the mourner's kaddish in Hebrew (on the right side of the page) with an English pronunciation guide on the left. A commonly used translation into English is also supplied below it, as well as a video recitation of the prayer.
The prayer actually comes from the ancient Aramaic language so translations and pronunciations vary.
There are also different traditions and pronunciations between Ashkenazic, Sephardic, and contemporary spoken Hebrew recitations of the prayer...check with your local congregation to see the preferred method(s). Contemporary Israeli Hebrew favors a Sephardic pronunciation.
English Pronuncation Hebrew text
Glorified and sanctified be God's great name throughout the world which He has created according to His will. May He establish His kingdom in your lifetime and during your days, and within the life of the entire House of Israel, speedily and soon; and say, Amen.
May His great name be blessed forever and to all eternity.
Blessed and praised, glorified and exalted, extolled and honored, adored and lauded be the name of the Holy One, blessed be He, beyond all the blessings and hymns, praises and consolations that are ever spoken in the world; and say, Amen.
May there be abundant peace from heaven, and life, for us and for all Israel; and say, Amen.
He who creates peace in His celestial heights, may He create peace for us and for all Israel; and say, Amen.
Here is a nice YouTube video showing the prayer being slowly recited so you can hear one type of pronunciation and see concurrently both the Hebrew and an English translation during the recitation.