I've always enjoyed the "Mental Math" section of the "Mentat Wiki": http://www.ludism.org/mentat/ http://www.ludism.org/mentat/ It covers 'tricks' for quickly

I've always enjoyed the "Mental Math" section of the "Mentat Wiki": http://www.ludism.org/mentat/ http://www.ludism.org/mentat/ It covers 'tricks' for quickly and accurately calculating squares, cubes, logs and roots (up to fifth root). Worth a look.