(Mostly Math Related)
http://www.cpm.org - website of resources for the textbook that we use; specifically helpful are the Parent Guides and Skill Builders worksheets that are in the Parent Section, under the heading of CPM Resources.
http://www.cpm.org/students/homework - homework help for every homework problem from CPM (textbooks used in my classes)
http://www.shodor.org/interactivate/activities/ - interactive online simulators of math concepts
http://www.education-world.com/math/ - Lesson Plan ideas – mostly for teachers
http://www.aaamath.com/ - Math Practice Problems
http://www.aplusmath.com/ - Math Practice Problems
http://mathforum.org/dr.math/dr-math.html - Ask Dr. Math
http://www.figurethis.org/ - Math Challenges
http://www.mcs.surrey.ac.uk/Personal/R.Knott/Fibonacci/fib.html - Fibonacci and the Golden Ratio
http://cte.jhu.edu/techacademy/web/2000/heal/mathsites.htm - cool math sites
http://www.theproblemsite.com/problems/mathhs/ - hs math challenge problems
http://www2.edc.org/makingmath/handbook/Teacher/Proof/Proof.asp - what are proofs?
http://www.regentsprep.org/Regents/math/ALGEBRA/PracticeTests/PracticeTests.htm - Algebra I final exam practice tests
http://www.regentsprep.org/Regents/math/geometry/math-GEOMETRY.htm - Geometry final exam review material
http://regentsprep.org/Regents/math/algtrig/math-algtrig.htm - Algebra 2 final exam review material
http://www.purplemath.com/modules/index.htm - Algebra I & Algebra 2 topics for review or tutoring
http://www.ams.org/mathmedia/ - math in the news
http://webquest.org/search/index.php - webquest search
http://www.pbs.org/teachers/mathline/lessonplans/search_9-12.shtm - PBS math video activity search for 9-12 math
http://nlvm.usu.edu/en/nav/grade_g_4.html - virtual manipulatives
http://score.kings.k12.ca.us/real.world.html - real world math applications
http://www.pinkmonkey.com/studyguides/studyguidesmain.asp - study guides for many subjects
http://www.despair.com - comical motivational? sayings