States of Matter - http://www.harcourtschool.com/activity/states_of_matter/ 

Simple interactive illustration of particles in solid, liquid, and gas states

What is Matter?(Gr.4) - http://www.nyu.edu/pages/mathmol/textbook/statesofmatter.html 

Simple written explanation and examples of each state of matter

BrainPop Movie - http://www.brainpop.com/science/matter/statesofmatter/ 

Short movie about the states of matter at Brainpop.com. (You can only view 2 a day per computer, unless you pay to join, so plan carefully.)

Chem4Kids - http://www.chem4kids.com/ 

Detailed information on topics including matter, atoms, elements, reactions, etc.

States of Matter Powerpoint - http://teach.fcps.net/trt18/3%20states%20of%20matter.ppt 

Reviews definitions and examples of each state of matter

Outrageous Ooze - http://www.exploratorium.edu/science_explorer/ooze.html 

Recipe for ooze. It can’t decide if it is a liquid or a solid.

Tech Topics: Matter - http://www.thetech.org/exhibits/online/topics/50a.html 

Short bits of information on matter, includes activities such as making ooze under States of Matter

Blue Goo - http://www.nationalgeographic.com/ngkids/trythis/try1.html 

Recipe for blue goo

Exploring Solids, Liquids, and Gas - http://partnership.svsu.edu/curriculum/k12/sciencelabs/solids.htm

A lab activity with printable worksheet.

Solids, Liquids, Gas Quiz - http://www.sciencentre.qld.gov.au/do&discover/test/solid.htm

Online 10 question quiz.  (Middle school level.)

3 States of Matter - http://ksnn.larc.nasa.gov/k2newsbreaks.html

A 60-second animated video clip from NASA on the 3 states of water. Also accompanied by activities for each grade level, K-2.