To help my oldest child learn her math facts, I have written two adventure stories. One teaches addition facts in the context of traveling to different parts of the world. The second, which I just finished, teaches multiplication facts in the context of traveling through time and space (but only on Earth). My daughters are assisting me with the task of illustrating them.
To share the stories with a wider audience, we are "self-publishing" them on Amazon.com. I just uploaded the first book this afternoon. It is called Adding Adventure to Life. The book is about as cheap as it can be ($0.99 for the first one), but it's so fun to see one's own nom de plume in print! (I used a pseudonym because my children are still young, and I want to protect their privacy.) Maybe by summer, we'll have earned enough to go out for ice cream. :)
Here's the link to the book if you are interested in seeing what a self-published e-book looks like on Amazon.com. Or if you feel like donating to an ice cream fund. Either one works.