WhyDoMath:

Enigma Project
http://www.enigma.maths.org/main/
The Enigma Project travels all over the United Kingdom and abroad, visiting over 100 schools and organizations, reaching over 12,000 people of all ages every year. It is part of the Millennium Mathematics Project at the University of Cambridge, aimed at inspiring students in math, science, and history through codes and code breaking.

Goudreau Museum of Mathematics in Art and Science
http://www.mathmuseum.org/
Promotes and encourages interest in mathematics for everyone, regardless of age or mathematical background.

HowStuffWorks - Science
http://science.howstuffworks.com/
HowStuffWorks is the award-winning source of credible, unbiased, and easy-to-understand explanations of how the world actually works. With comprehensive articles, helpful graphics and informative videos, topics are presented clearly, simply, and objectively. The premise is to demystify the world and do it in a simple, clear-cut way that anyone can understand.

MAA Distinguished Lecture Series
http://www.maa.org/dist-lecture/past-lectures.html
The MAA, with the generous support of the NSA, presents a series of public lectures featuring some of the foremost experts within the field of mathematics, known for their ability to make current mathematical ideas accessible to non-specialists. It provides a learning opportunity for both professionals and students, as well as anyone interested in learning more about current trends in mathematics and the relationship between mathematics and broader scientific, engineering and technological endeavors. 

MacTutor History of Mathematics archive
http://turnbull.dcs.st-and.ac.uk/~history/
The MacTutor History of Mathematics archive is an integrated collection of over 1,000 biographies and historical articles of a mathematical nature, alongside interactive birthplace maps and the famous curve applet.

Math Archives
http://archives.math.utk.edu/
Teaching materials, software, web links, and other material organized by mathematical topics and available through a searchable database.

Math Forum@Drexel
http://www.mathforum.org/
Drexel University website geared towards students.
 
Math in the Media
http://www.ams.org/mathmedia/
Math in the Media is a monthly magazine from the American Mathematical Society (AMS).

Math Matters, Apply It!
http://www.siam.org/careers/matters.php
Math Matters, Apply It! is an applied mathematics awareness campaign, created for anyone who wants to know more about the mathematics behind everyday life and the technologies we encounter.
 
Mathematical Moments
http://www.ams.org/mathmoments
The Mathematical Moments program of the AMS promotes appreciation and understanding of the role mathematics plays in science, nature, technology, and human culture. This series of PDFs, some of which include embedded audio presentations, can be used as teaching resources and to promote awareness of mathematics to students, colleagues, and attendees at meetings and special events.

Mathematical Resources
http://www.math.okstate.edu/~wrightd/useful/index.html
Maintained by Oklahoma State.

Mathematics Awareness Month
http://www.mathaware.org/index.html
Mathematics Awareness Month is held each year in April. Its goal is to increase public understanding of and appreciation for mathematics. Mathematics Awareness Month is sponsored each year by the Joint Policy Board for Mathematics to recognize the importance of mathematics through written materials and an accompanying poster that highlight mathematical developments and applications in a particular area.

MathSearch
http://www.maths.usyd.edu.au/MathSearch.html
A collection of over 200,000 documents on English-language mathematics and statistics servers across the Web.

Millennium Mathematics Project (MMP)
http://mmp.maths.org/
The Millennium Mathematics Project aims to support math education for pupils of all abilities from ages 5 to 19 and promote the development of mathematical skills and understanding, particularly through enrichment and extension activities beyond the school curriculum. It also engages in activities designed to improve the public understanding and awareness of mathematics.

Mu Alpha Theta
http://mualphatheta.org/
Mu Alpha Theta is the national honor society for mathematics students attending high schools and junior colleges.

NSF Mathematical Sciences Institutes
http://www.mathinstitutes.org/
A collaboration of the seven NSF-funded Mathematical Sciences Institutes, this web portal features an event database and a growing collection of research highlights focusing on scientific research findings from the Institutes.

Plus Magazine
http://plus.maths.org/
Based in the U.K., Plus is an Internet magazine which aims to introduce readers to the beauty and the practical applications of mathematics.

S.O.S. MATHematics
http://www.sosmath.com/
S.O.S. MATHematics is a free resource for math review material from algebra to differential equations. This study site for high school, college students, and adult learners provides 2,500 math pages filled with short and easy-to-understand explanations for help with homework, to refresh the memory, for test preparation, etc.

When Will I Use Math?
www.whenwilliusemath.com
A website from the Brigham Young University Math Department with support from MAA includes mathematical careers, salaries, and job requirements, as well as tips and advice on how to succeed in mathematics, introductions to new mathematical discoveries, and even tidbits on the role math plays in pop-culture. It includes resources for teachers, parents, and others who want to help people appreciate mathematics. 

Wolfram MathWorld
http://mathworld.wolfram.com/
MathWorld is the web's most extensive mathematical resource, provided as a free service to the world's mathematics and Internet communities as part of a commitment to education and educational outreach by Wolfram Research, makers of Mathematica.

Yahoo Mathematics Directory
http://dir.yahoo.com/Science/mathematics/
Yahoo’s directory of websites related to mathematics.