Transverse waves are the easiest to picture, because syou can visualize and often see material moving. Essential knowledge: Transverse, Longitudinal, Torsional and Love Waves.
Transverse waves
Longitudinal waves
sound waves: http://onlinetonegenerator.com/
Torsional waves
Torsional wave demo – sticks, tape and jellie babies
Tacoma Narrows Bridge Collapse
Love waves