Math Mammoth is another good program for elementary ages. IMO, it is comparable in quality to Singapore Math. The books are available in print, via download, or on CDs: mathmammoth.com . Math Mammoth costs a little less. Om the other hand, it does not have additional books like Singapore Math's 'Intensive Practice', etc.

And thank you for the reviews, Aquinas! I wish I could find such useful info on other subjects!