MATHEMATICS
Ask Dr. Math. http://forum.swarthmore.edu/dr.math/ A resources for K-12 math questions.
The Math Forum. http://forum.swarthmore.edu
The Mathematics Archives. http://atchives.math.utk.edu/k12.html Contains materials for teaching mathematics at the K-12 level.
MegaMathematics. www.c3.lanl.gov/mega-math
Includes entertaining projects which deal with math in unusual ways.
SCIENCE
Frank Potter's Science Gems. http://www-sci.lib.uci.edu/SEP/SEP.html Contains resources sorted by category, subcategory and grade level.
The Franklin Institute Science Museum. http://sln.fi.edu/tfi/ Offers a variety of science-related links and projects.
Hands On Children's Museum Ocean Odyssey Hot List. www.wln.com/~deltapac/ocean_od.html
SciEd: Science and Mathematics Education Resources. http://www-hpcc.astro.washington.edu/scied/science.html
Volcano World. http://volcan.und.nodak.edu
The Why Files. http://whyfiles.news.wisc.edu The science behind the news funded by the National Science Foundation.
Windows to the Universe. www.windows.umich.edu Provides information on astronomy-related resources.
The Yuckiest Site on the Internet. www.nj.com/yucky Explains strange features by means of science.