Anamorphic Art
http://users.skynet.be/J.Beever/pave.htm

Congruence Rules for Geometry:  
Experiment with S.S.S, S.A.S, A.S.A and SSA
http://matti.usu.edu/nlvm/nav/frames_asid_165_g_4_t_3.html?open=instructions

Fractions
Visualize Common Divisors
http://matti.usu.edu/nlvm/nav/frames_asid_106_g_4_t_1.html

Graphing Utility:
http://matti.usu.edu/nlvm/nav/frames_asid_109_g_4_t_1.html?open=activities

Pascal Triangle:
Interesting Relationships in Pascals Triangle
http://matti.usu.edu/nlvm/nav/frames_asid_181_g_4_t_1.html?open=activities

Percentages:
Relations among percentages, fractions and decimals.
http://matti.usu.edu/nlvm/nav/frames_asid_160_g_4_t_1.html?open=activities

Geometric Turtle Graphics:
programming/geometry
http://matti.usu.edu/nlvm/nav/frames_asid_178_g_4_t_1.html?open=activities

Sieve of Erosthenes
http://matti.usu.edu/nlvm/nav/frames_asid_158_g_4_t_1.html?open=instructions

Mastermind
http://matti.usu.edu/nlvm/nav/frames_asid_179_g_4_t_1.html?open=instructions

Fill and Pour
http://matti.usu.edu/nlvm/nav/frames_asid_273_g_4_t_4.html

Master Math Mentor 
http://www.mastermathmentor.com/

inattention blindness
http://viscog.beckman.illinois.edu/flashmovie/15.php