Maths Games on Internet
My son (grade 2) is usually more keen to complete his homework if he gets 15 mins or so of maths/educational games at the end.
He likes the games at sites like:
www.mathletics.com.au
http://www.coolmath4kids.com
http://www.primarygames.com/math.htm
Even some of the maths training Nintendo DS games are a great educational reward once the kids have completed their homework.