Scholastic Online Activities - Divided into K-2 and 3-5 online activities in Language Arts, Math, Social Studies, and Science. 50+ activities at 15-30 minutes each.
Watch, Know, Learn - Free educational videos for K-12, categorized by core subjects, computers, history, life skills, physical and health education, holidays and special occasions, hobbies and crafts, and many more.
Cookie.com - Online books, games and acvitites, and printable worksheets.
Word Dynamo - Create your own vocabulary lists with definitions and turn them into tests or games. Free registration is required.