Learning Science.org

http://learningscience.org/

Basic physical science, life science, environmental science, health, geology, biology, and chemistry for grades K-12.

Math ABC

http://www.mathabc.com/

Interactive math website for kids in 1st to 6th grade.

Math In English

http://www.mathinenglish.com/menuWorkbooksI.php

Grades 1-6 up to pre algebra.

Features:
Worksheets
Workbooks
Problem sets
Puzzles

Sensible Math Education - Worksheets

http://www.sensible-math-education.com/free-printable-math-worksheets.html

K-8th grade worksheets

Don Potter Arithmetic Textbook

http://www.donpotter.net/math.htm

Online arithmetic textbook.

AAA Math

http://www.aaamath.com/B/index.htm

Study site for K-8th grade with a Spanish version.

Subjects Covered:
K-8th grade math topics up to geometry and algebra
Spelling
Vocabulary
States of the USA
World Nations

Features:
Interactive practice with games and pictures
Customizable spelling and vocabulary lists (1st-8th grade)
Math articles
Flags, capitals, states, and nations worksheets and exercises