Helpful for teaching reading: http://reading.ecb.org/
(There's a section for kids and teachers)

AAA Spelling: Practice Spelling Words: www.AAASpell.com

Math Sites:

www.aaamath.com

www.aplusmath.com

http://www.funbrain.com/fract/index.htmlhttp://www.funbrain.com/fract/index.html

Kidport: www.kidport.com/default.htm
  Educational games and activities in science, social studies, language arts, and creative arts.

http://funschool.kaboose.com/
This is a site with all kinds of educational games. If you scroll down to the bottom you can click on activities that are age level appropriates.

http://www.pdoodle.com/funhouse.html
This is a fun site that lets you play games, read funny jokes, create a puzzle, and play arcade games.

http://pbskids.org/
This is another fun educational site. The PBS kids' characters are on this site. Pick a character to see the fun things you can do.