Students use the concept of Venn Diagrams to place each animal in the correct enclosure.
http://pbskids.org/cyberchase/games/logic/

Two mind reading activities. The first one can be explained using knowledge of linear expressions, while the second one is just a bit of fun.

A triangle is made up of four pieces. Move the pieces around to make a new congruent triangle. Except the new triangle is missing one square unit! Where did it go?

Your calculator is missing some of its keys! Which answers can you still get?
Six levels, from easy to challenging!

Alphametics are arithmetic puzzles in which each letter represents a different digit. Use your knowledge of place value and numbers to solve the puzzle.

This is a very cool and very engrossing set of puzzles. Use the cubes to build the shape that has the correct front, top and side views. Now try to solve the puzzle using the minimum number of cubes. The shape can be spun in 3-dimensions. Three thumbs up!

http://www.fi.uu.nl/toepassingen/02015/toepassing_wisweb.en.html

Use a spreadsheet to find out how long it will take the classes to save 1,000,000 pennies. From The Math Forum POW.

An Activboard flipchart for the classic game of Nim. Players take turns removing chips from one row of the board. The winner is the person who chooses the last chip.

Hint: do you know your binary numbers?

Paper Pool is rich interesting task that requires students to investigate, make conjectures and then test and verify conjectures. Depending on the question being investigated, it is suitable for students from Year 3 to Year 12. There are five prepared lessons to accompany this interactive task, so your prep is largely done for you!
http://illuminations.nctm.org/ActivityDetail.aspx?ID=28

A nice Java implementation of the classic Mastermind game.
http://nlvm.usu.edu/en/nav/frames_asid_288_g_1_t_1.html?open=instruction...