Doubles! Doubles! Doubles!
Gotta know the whole family (ie 4+4=8 AND 8-4=4 all the way up to 9+9=18 and 18-9=9. Then...60 + 60 and 90 +90!)
http://www.adrianbruce.com/math/addition/item/16-doubles-maths-game.html
http://www.quia.com/jg/325021.html
http://www.adrianbruce.com/math/addition/item/16-doubles-maths-game.html
http://www.quia.com/jg/325021.html