Forget about buying those $1.99 flash cards from Wal-Mart if you or your child are in need of some mutliplication facts work. Mental Maths by Trilliarden has a fun and exciting system for exercising your brain and improving mental math ability.
iPhone and iPad apps tagged "math app."
Brain Thaw: Got A Cool Head for Math?
Brain Thaw - I feel comfortable saying that there's nothing in the world that can't be improved at least a little bit by adding penguins. They're cute! They waddle! They... eat numbers? In Brain Thaw, they do.
Math Geeks will Love The Graphing Calculator App
There are a number of tools to graph equations in the App Store, but the "Graphing Calculator" by Gabor Nagy has the dual advantage of being both excellent and free. As a math major myself, and a former user of programs such as "Mathematica", I was genuinely impressed with the interface and functionality of this tool.