I'm taking this answer directly from goodsecurityquestions.com website, as referenced on the Security StackExchange site.

The term "security questions" is a misnomer. Security questions create a potential hole or breach in security by providing ways for unauthorized users to gain access if the answer can be discovered. Hopefully, security experts will find better ways of retrieving forgotten passwords or verifying identification during login, but until then security questions will likely prevail.

Thus, security questions have both benefits and liabilities. Poor questions create security breaches and confusion and cost money in support calls. Good security questions can be useful in the current environment, but are not common.

However, there really are NO GOOD security questions; only fair or bad questions. "Good" gives the impression that these questions are acceptable and protect the user. The reality is, security questions present an opportunity for breach and even the best security questions are not good enough to screen out all attacks. There is a trade-off; self-service vs. security risks.

Social networking (Facebook, MySpace, Twitter, personal blogs, LinkedIn) are creating more of a risk for security questions. People are generously telling all about themselves, their history, likes, favorites, and more. It easier now to find information on people.

But to actually answer your question, that site provides a list that they say are better than others that meet the criteria of:

Good security questions have four common characteristics. The answer to a good security question:

1. cannot be easily guessed or researched (safe),
2. doesn't change over time (stable),
3. is memorable,
4. is definitive or simple.

And those questions are:

• What was your childhood nickname?
• In what city did you meet your spouse/significant other?
• What is the name of your favorite childhood friend?
• What street did you live on in third grade?
• What is your oldest sibling’s birthday month and year? (e.g., January 1900)
• What is the middle name of your oldest child?
• What is your oldest sibling's middle name?
• What school did you attend for sixth grade?
• What was your childhood phone number including area code? (e.g., 000-000-0000)
• What is your oldest cousin's first and last name?
• What was the name of your first stuffed animal?
• In what city or town did your mother and father meet?
• Where were you when you had your first kiss?
• What is the first name of the boy or girl that you first kissed?
• What was the last name of your third grade teacher?
• In what city does your nearest sibling live?
• What is your oldest brother’s birthday month and year? (e.g., January 1900)
• What is your maternal grandmother's maiden name?
• In what city or town was your first job?
• What is the name of the place your wedding reception was held?
• What is the name of a college you applied to but didn't attend?
• Where were you when you first heard about 9/11?