You can find out more about maths games on wikipedia.
Top 5 Mental Maths Book Every "Genius" Reads
Secrets of Mental Math: The Mathemagician's Guide to Lightning Calculation and Amazing Math Tricks
Number Talks: Helping Children Build Mental Math and Computation Strategies, Grades K-5
Mental Math in Junior High / Grades 7-9
Mental Math in the Primary Grades 01614
Mental Math in the Middle Grades