PBS
Pbs: Buoyancy Basics
NOVA explores the basic principle of buoyancy. Also included at this site are some interesting brain-teasers related to the topic.
Science and Mathematics Initiative for Learning Enhancement (SMILE)
Smile: Density in Relation to Float and Sink
Students find the densities of objects based on sinking or floating in this activity that demonstrates Archimedes Principle.
Michigan Reach Out
University of Michigan: Paper Clip Sailing
Basic experiment that helps learners learn about surface tension.