Well, I think it'd be useful to collect right here all the websites that we consider useful (this means, with LaTeX; a math forum without LaTeX is not a math one).

MathLinks

FMAT (spanish forum, I take part there )

S.O.S. Math

Post useful sites that you know!

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• Got trouble with LaTeX? Take a look.
  
• Make your partial integration (aka integration by parts) faster. Click here.
  
• How to prove limits by the definition.

This one.

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And he (Elisha) went up from thence unto Bethel: and as he was going up by the way, there came forth little children out of the city, and mocked him, and said unto him, "Go up, thou bald head"; "go up, thou bald head". And he turned back, and looked on them, and cursed them in the name of the Lord. And there came forth two she-bears out of the wood, and tore up forty and two children of them.
Second Kings 2: 23-24

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.

Other sites with Latex:

Foro de Geometría
http://www.maths-forum.com/index.php? (in French)
Math Is Fun Forum
Physics Help and Math Help - Physics Forums (contain also math topics)
Problema săptămânii (in Romanian)