Everyday Math Student Page! Has games and activities. There is some updating going on right now... It is also easy to find a parent section. This is the official site. http://everydaymath.uchicago.edu/students/index.shtml
For researching or learning new information, try this site. It is also from Scholastic Book Club. Scholastic School Activities
Free math games to download! Practice math facts! You'll have to search around for the free ones, they are mixed in with the programs you have to buy. http://www.pcdistrict.com/addition-and-subtraction-sitesearch-230.html
This is an AWESOME math game site! Funbrain!