The Kaboose Network - Has many activities and games for preschoolers through 6th grade.
Kids Psyche - Games for children ages 1-5.
Kids Domain - All kinds of resources for children. Ex. Brain Builders, Download games, Online games, Icons, sports and a surf safe site.
Pre-school Library - The StoryPlace Pre-school Library is full of great activities for you to explore. You pick a theme and it gives you 5 different options to do with it. There is an online story, an online activity, an activity to take home, suggested readings and Parent's activities.
The Learning Planet - This webpage has activities and resources for preschool through 6th grade. It is a website that you have to subscribe to (for a fee).
Otto Club - Part of AAA, a website containing Otto's Playland. It is a way to play all sorts of games, but safely. Teaches safety.