You know, a math site that has been around for quite a while and has helped a lot is mathnerds.com
The thing is, considering the traffic they get, they absolutely refuse to implement LaTex. Why, I don't know?.
I asked why and one reply I got was it "cost too much". Come on
You still have to type it out the primitive, behind-the-times way, just using what's on the keyboard.
That site works differently than most. You have to be approved to answer questions which are posted by first answering some test questions in the category you wish to answer questions in.