Bride's Magazine wrote a very interesting article entitled the "8 Questions to Ask Your Partner Before Marriage that will Help Prevent Divorce".
These are the 8 Questions:
What are your financial goals and how can we try to reach them?
How can I help you when you are stressed?
Do you want children and what would you do if we struggle to get pregnant?
What's your communication style?
What are your Deal-Breakers?
How much alone time do you need?
What's your biggest fear?
What does marriage mean to you?
I've only listed the eight questions but for those considering marriage, it is a very enlightening read.