Homeschool Tracking and Scheduling

Very thorough--even allows you to count extracurricular stuff (like computer programming, reading, or other hobbies) toward your required hours.

http://www.homeschoolskedtrack.com/

Freely Educate

Great site that also mines the web for free homeschooling resources:

http://www.freelyeducate.com/

How am I different from a bird?

AWESOME preschool/kindergarten (or even for older kids) lesson on the characteristics of mammals vs birds. One of the funnest and best I've seen, actually:

http://outsidemom.com/2011/06/how-am-i-different-from-a-bird/

Melody Street

Classical music games, videos, radio, etc.

http://melodystreet.com/INDEX/live/

Simple English Wikipedia

This is a fantastic resource. It is language-filtered for simplicity, and appropriate for children linguistically.  It is NOT content-filtered, so, as with all Wikia, supervise use.

http://simple.wikipedia.org/wiki/Main_Page

Preschool Biology Course, on a calendar

This is very very cool, complete, and would appeal to preK-3rd graders, or even older if you present it right.

http://grassstainguru.com/wp-content/uploads/2011/06/calendar_nature.pdf

How Plasma Displays Work

http://electronics.howstuffworks.com/plasma-display.htm

Where does our food come from

http://sprouts.com/COOL/#

Is there such a thing as a Jellyfish?

http://youtu.be/3HzFiQFFQYw

Basic Multiplication practice sheets

http://math.about.com/od/multiplication/ig/Times-Tables-Worksheets/

or online:
http://www.oswego.org/ocsd-web/games/Mathmagician/mathsmulti.html

http://www.mrmyers.org/Math_Mania/ttmult.html

http://www.multiplication.com/quizzes.htm