Quora – A site for mostly professional questions about science, economics, movies or anything else. Currently owned by Wikipedia founder Jimmy Wales (who sometimes answers questions too)!
Question.com – Questions and answers in any category. Although it has a good name, users are not as active as on the other sites listed here.
Yahoo! Answers – Probably the most popular one with millions of possible users who can answer your questions (anyone can participate who has a Yahoo! account).
The AnswerBank – Questions about sports new and entertainment.
Askreddit – Subreddit for questions to the reddit community.
ELI5 – Explain Me Like I’m 5. Ask any hard science question and receive answers in Layman’s term.
AMA – Ask Me Anything. Ask famous people or someone with interesting experiences or job anything.
No Stupid Questions – Another subreddit where you can ask questions. Here you can ask any question and no one will be rude to you for not knowing the answer.