The following sites could be used with small groups of students to enhance Literacy and Numeracy skills as as well to simply find ideas for fun activities.
Intensive Learning - ideas for using the internet to enhance Mathematics, Writing and Reading. This has been redesigned for SSO use.
K-12 Education - search engine with lots of different subjects listed.
Working with Girls - a site with lots of other sites to enhance girls' education as well as to discuss girls' issues.
Sites for Kids - tons of different sites for primary aged kids
Games for Kids - online and off.
Funology Web - tons of great things to do while learning on the web, including quizzes and games.
4Recipes - if you're looking for something to cook.
Golden Books Website - links to Barbie and Bob the builder etc.
Elmers.com - project help for teachers and students
Crayola Art Lessons Site - lots of ideas and fun.
Ask Dr. Universe - questions of a scientific nature answered in a fun way.
Becky's Campfire Songbook - songs for kids
Word Central - daily buzzword
Betty Crocker.com! - recipe fun