Level one is a nice not-too-hard introduction to tangram puzzles. This puzzle at this level is good for the littlies, I think.

The higher levels are still reasonably easy.

http://www.channel4learning.net/sites/puzzlemaths/tangrams.shtml

This excellent ActivBoard flipchart includes 15 Mathematical activities to teach the subject of shapes and space.

It covers a wide range of areas such as transformations & reflections, the properties of shapes and using quadrilaterals. Three thumbs up!

The flipchart can be found here:
http://www.prometheanplanet.com/uk/server/show/ConResource.13733

If you are not yet a member of Promethean Planet, you will first have to register here:
http://www.prometheanplanet.com/uk/server/show/nav.914

If you want to view the activities and have some interactivity with them, but you don't have the ActivStudio software, you can download the free Viewer from here:
http://www.mypromethean.com/uk/server/show/ConWebDoc.2974

You are given a circle of radius 1 unit and two circles of radius a and b which touch each other and also touch the unit circle. Prove that you can always draw a 'flower' with six petals with the unit circle in the middle, and six circles around it having radii
a, b, b/a, 1/a, 1/b and a/b
such that each outer circle touches the unit circle and the two circles on either side of it.
http://nrich.maths.org/public/viewer.php?obj_id=2153

Naomi has a triangle which is blue on one side and yellow on the other. It has a dot in one corner on each side.

How many ways are there of posting this triangle through a triangular shaped slot?

http://nrich.maths.org/public/viewer.php?obj_id=2644

How many different triangles can you draw on a circular pegboard which has four equally spaced pegs? What are the angles of each triangle?

If you have a six-peg circular pegboard, how many different triangles are possible now? What are their angles?

How many different triangles could you draw on an eight-peg board?
Can you find the angles of each?

http://nrich.maths.org/public/viewer.php?obj_id=2850

A wonderful interactive implementation of tesselations from the NRich website.
http://nrich.maths.org/public/viewer.php?obj_id=6069

This flash program could be used to introduce simple transformations to the littlies, or an an application of group theory to senior high school students. How cool is that!
http://nrich.maths.org/public/viewer.php?obj_id=5560

An interactive animation demonstrating how parallel vectors link a triangle and its translated image.
http://www.yenka.com/freecontent/item.action?quick=hd#

A simple but clear interactive animation demonstrating how a parallelogram is formed from a rectangle.
http://www.yenka.com/freecontent/item.action?quick=di#

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