Here are several completely free classic math books that you can download from the Google Books archive!
Each book by Franklin Hoyt and Harriet Peet is very practical and would be a great addition to any math curriculum.
Click here to download the book First Year In Numbers [1] (grade 2)
Click here to download Everyday Arithmetic Book 1 [2] (grades 3 & 4)
Click here to download Everyday Arithmetic Book 2 [3] (grades 5 & 6)
Click here to download Everyday Arithmetic Book 3 [4] (grades 7 & 8)
A Course Of Study In Everyday Arithmetic + Answer Guide To Previous Books [5]