Whenever possible, I like to substitute online games for repetitious math homework, such as multiplication drills and such. Following are the three best websites I could find for elementary level math games to play online. Each website is well organized, has a large collection of games, and has multiple levels of games so that you can tailor the activities for your little learner. And, of course, they're all free, with few or no ads cluttering up their site.
1st up - fun4thebrain.com. Page after page after page of truly entertaining and well-designed games, most with customizable levels. Website is divided up in sections for multiplication, addition, division, and subtraction. This is ds9's favorite math website.
2nd up - shppardsoftware.com. There are games on this website that cover the full spectrum of math, such as operations, money, geometry, time, and much more! While the website is extremely easy to navigate, I wished that some of the games were more customizable as far as their skill level is. But, as it is, most of the games are RIGHT at ds9's skill level, so I can't really complain. :) Also, this website has a LOT of other really well-made games in many other academic areas as well. I might have to explore the website further and give you a more extensive report on it another day.
3rd up - funbrain.com - math section. This section of their website has all their math games listed out according to possible grade level, which is really handy. You can also filter the games by a keyword search, such as multiplication or fractions, so you can find exactly what you're looking for. Fun, highly customizable games! There are also games covering a number of other subjects available from their home page, though not quite as academic as ShepardSoftware.
Know of a great math games website? Comment and let us all know about it!