I recommend Ask MetaFilter which is 100x better than Yahoo Answers, AnswerBag and any other question site I've used. I use MetaFilter almost entirely for the Ask MetaFilter portion of the site.
The main reason I like it is because:
. It's virtually spam-free (a $5 signup fee is pretty much fully responsible for this)
. It has an intelligent user-base
. It's minimalistic
. You tend to get way more responses to your questions than you do on competing sites (it's not rare to get 50 or more responses to your questions)
I've been a fan of the site for a long time now. The only drawback is that you can only ask a single question per week. However, you could ask more than one question a week if you were to sign up for multiple accounts, but I'm not sure if you'd get in trouble if you'd get caught. You probably would, but if you choose to do this, maybe space out your registrations; don't sign up for multiple accounts all at once. You can actually ask more than one question in the span of one week if you wish to, but you have to PM a staff member of the site if you want to do this. But I'm sure staff would eventually get annoyed with you if you were to PM them constantly asking them to allow you to post extra questions.
Anyway, I decided I'd create this topic since I always have people telling me that they asked a question on Yahoo Answers which, IMO, is an awful site to ask questions on. Let's put it this way: The users there aren't very bright. The $5 fee to get into MetaFilter may be a turn-off for some people, but honestly - it's brilliant that the owner of that site made it this way. The majority of trolls and spammers would never bother paying money to troll and/or spam a site.