Students choose a particular Venn Diagram and then choose the geometric property for each region. They then have to place the geometric shapes in the correct region. Two thumbs up!
http://illuminations.nctm.org/ActivityDetail.aspx?ID=34

The Golden Rectangle is a plot created by starting with a rectangle, chopping off successive squares, and drawing quarter circles with a radius equal to the side of the square that was cut.
http://nlvm.usu.edu/en/nav/frames_asid_133_g_3_t_1.html?open=instruction...

Choose some shapes and try to tesselate the plane with them.
http://nlvm.usu.edu/en/nav/frames_asid_163_g_1_t_3.html?open=activities&...

Tangrams are a versatile manipulative. They can be used to build understanding of geometry, fractions, area and other topics. This is a Java implementation of tangrams.
http://nlvm.usu.edu/en/nav/frames_asid_268_g_1_t_3.html?open=activities&...

Attribute blocks can be used to help students understand colour, shape and size. This is a lovely Java implementation of this manipulative.
http://nlvm.usu.edu/en/nav/frames_asid_270_g_1_t_3.html?open=instruction...

Pattern blocks can be used to teach patterns and algebra, symmetry, fraction concepts and other math topics.
http://nlvm.usu.edu/en/nav/frames_asid_169_g_1_t_2.html?open=activities&...

See
http://math.rice.edu/~lanius/Patterns/notes.html
and
http://mason.gmu.edu/~mmankus/talks/PBlocks/pbact/other.htm
for some ideas on how to use this manipulative in the classroom. This is a nice Jave implementation of this manipulative.

A collection of matching games, including multiplication tables, addition tables, equivalent fractions, and fraction-to-percent conversions. These are flash files.
The answers are randomly placed so each game can be used over and over.
http://www.subtangent.com/maths/games-dl/matching.zip