The following question-answer sites are very popular and hope it becomes helpful to you in getting the best solution on your query and giving your suggestion or advice on relevant topic.
1) http://answers.yahoo.com/
2) http://wiki.answers.com/
3) http://www.askpedia.com/
4) http://www.answerflip.com/
5) http://aolanswers.com/
6) http://www.answerbag.com/
7) http://www.mylot.com/
8) http://www.justanswer.com/
9) http://www.knowbrainers.com/
10) http://www.fluther.com/