Practice your math facts online. Try to beat your best time! honorpoint.com
Math Playground Have fun practicing those facts or reviewing skills for the next test http://www.mathplayground.com/
Practice your math skills without getting your hands dirty! http://nlvm.usu.edu/
Free Rice Do something good for something else while you build your skills in language arts and math! http://www.freerice.com
Spaghetti Book Club Read book reviews by kids like you before you head off to the library! http://spaghettibookclub.org/