There are many ideas for students to investigate in categories such as Numbers and Geometry . Check out 80 different polyhedra with your students. Watch an animation of each one choosing from a well designed Visual Index . Line, face and edge information is also available. There are also many links and descriptions of other useful sites such as Statistics Canada .
New problems appear every month for the elementary student from all math strands.
The Replacing Trees problem is a good example relating the communication of a problem and environmental studies. Interactive Mathematics Miscellany and Puzzles A wealth of text, animation and resources can be found here but leave a lot of time for exploring for something at the elementary level. Most deal with higher level thinking. Check out Alexander Bogomolny's collections of puzzles and other people's sites . His Exchange might answer some of your questions.