Classic Arithmetics

http://www.donpotter.net/math.htm

A lot of word problems, stories of addition etc.

Thoughts on elementary math

http://www.mathedpage.org/early-math/early.html

Some parts can be a chore to read, but the various games/fun activity suggestions and the summary is really good on elementary math education (imho).

Games

Math

Volume (3-6, 6-9)

http://pbskids.org/cyberchase/games/liquidvolume/