MathNerds
MathNerds is a very nice math help site. On the site you can ask a question in a host of categories from grade school up through graduate level mathematics. The average response time to a question is currently 24-36 hours. Anyone needing help on a math problem should visit the site at www.mathnerds.com
MathNerds also has an extensive archive of questions and answers that you can search through.
In the interest of full disclosure I feel that I should point out that I have a vested interest in pushing you to MathNerds as I help to maintain the site.