A versatile number line flash program for whole numbers and decimals. From Ambleside Primary.
http://www.amblesideprimary.com/ambleweb/mentalmaths/numberlines.html

An interactive tangram from Ambleside Primary.
http://www.amblesideprimary.com/ambleweb/mentalmaths/tangram.html

This is a fun game from Ambleside Primary. Choose your level. Add the numbers in the bottom row to get numbers in the middle row. Then add the numbers in the middle row to get the answer at the top of the pyramid. Now check your answer. There are three levels - easy, medium and hard.
http://www.amblesideprimary.com/ambleweb/mentalmaths/pyramid.html

Type in the Input. The Function Machine applies the function and produces the Output. If you choose [Random], you will have to use some brainpower to figure out the hidden function.
http://www.amblesideprimary.com/ambleweb/mentalmaths/functionmachines.ht...

Linear Function Machine
With this function machine, you have to enter the correct linear function, using algebra.
http://www.shodor.org/interactivate/activities/LinearFunctMachine/

The Fractotron is a game designed by Year 6 students at Ambleside Primary School. The player has to decide (quickly!) if the fraction shown is bigger than 1/2, equal to 1/2 or smaller than 1/2/
http://www.amblesideprimary.com/ambleweb/mentalmaths/fractotron.html

A four person game (five if another student is the 'mouse-meister') from Abbleside Primary School that reinforces multiplication facts:
http://www.amblesideprimary.com/ambleweb/mentalmaths/gameshow.html

Here is a simpler version, with smaller numbers:
http://www.amblesideprimary.com/ambleweb/mentalmaths/gameshoweasy.html

And a similar game, also from Ambleside Primary School:
http://www.amblesideprimary.com/ambleweb/mentalmaths/tabletrees.html

A high quality video game that will help students learn their times tables, up to 12x12. The basic version (which is still excellent) is a free download. Students and schools can purchase the full version, which has even more cool graphics.

Main website: http://www.bigbrainz.com/index.php
Download page: http://www.bigbrainz.com/Download.html

This flash program shows the consistency of sample means from variously shaped populations. A student can change sample sizes, view raw data, choose samples singly or by the thousands, and observe changes as the sample numbers and populations change. It is also available as a stand-alone program (recommended for the classroom as it can be shown in full screen mode).

http://www.teacherlink.org/content/math/interactive/flash/sampling/sampl...

Line up the people in order of height. Then find the median, Q1 and Q3. For some reason they all look very cranky...
http://www.subtangent.com/maths/median-and-quartiles.php

You have some frogs on the left that move to the right, and some frogs on the right that can move to the left. Can you swap the positions of the frogs in the fewest number of moves? Investigate!
http://www.subtangent.com/maths/ig-leapfrog.php