These are some websites that have free worksheets on all subjects:

http://edhelpler.com/

http://www.abcteach.com/

http://www.enchantedlearning.com/Home.htm

a really fun math site:

http://www.whizz.us/

and starfall, which was recommended to you already, is a really wonderful site for learning to read, and pretty much up to third grade level. they have tons of activities, its pretty much a years worth of phonics materials in it.

as he advances in math skills, this game is excellent for learning the times table:

http://www.bigbrainz.com/

Finally, there's a lot of online classes for kids that have free trials, the majority have them, and the trials can be as long as two months for some of them.

Wisdom begins with wonder. – Socrates