SUMS Online offers software that is used in over 700 schools in the United Kingdom. The software consists of many math activities in Adobe Flash format. SUMS software works on Mac, Windows, and Pocket PC computers. Check out the sample activities SUMS offers in The Playground. SUMS activities are correlated with U.K. curriculum. The company is in the process of making their activities more U.S. friendly. Unfortunately, the software doesn't have built-in management or progress tracking. But, the software does offer valuable practice with interesting activities for students.
In fact, SUMS will give the first K12 school to apply from each recognized USA school board area a free two-year subscription to their online service (value $160 per year) along with free use for two years of the Pocket PC versions of the software (value $1 per handheld per year). Contact David McAll (email@example.com) at SUMS Online before Dec 31st 2006. The free offer will be the "Americanized" versions of SUMS activities, though you can see the U.K. demos in The Playground.
Full Disclosure: I work independently from any company. I do not receive money from the products I write about on this site. The exceptions are my book and other books linked to from this site through Amazon.com.