www.quizlet.com for vocabulary and writing skills and for math. It's amazing how spelling words and doing arithmetic problems suddenly became so addicting to my 8. y.o. as a result of using these online tools.
www.education.com/activity/ - It has lost of great activities subdivided into topics like math, science, cooking, arts and crafts and so on, for kids from kindergarten up. Many of the activities I looked at are truly fun. When you try to print they ask you to sign up, you don't have to if you don't want to, you can simply close that sign up window and the activity will print.