Another great site with learning games. This one seems to be completely free (I haven't used it a ton, so maybe I just didn't reach the free-use limit). Best of all, it has games for nearly every subject, and the games are categorized by grade and subject.

IXL has hundreds of Math related games, categorized by grade and topic. It is a subscription based site, but allows quite a few free uses, and even once you've used up your free practice for the day it refreshes and let you try again the next day.

Here's a textbook assigned in at least one other Gordon class. It presents a model of teaching mathematics that is far more engaging for students than what you and I likely remember. It's free by using your Gordon library number, so this could save you about $40 as it did for me.