The most basic diffusion device spreads, softens and reflects light back onto the subject, and comes
in white, silver or gold surfaces. You can also get translucent ones to shoot through.
Softboxes come in various sizes and produce more natural, window-like lighting, and can simulate a daylight sky if used overhead.
Metal dishes that come in various depths and diameters for direct, usually hard lighting.
A narrow cone that channels the flash light to a narrow beam - ideal for hair, for example.
A grid that narrows the angle of the flash, somewhat like a snoot.
A rim with four hinged side flaps, like a cardboard box, which can be angled to control the spread of light.
Stands need to be sturdy enough not to become unstable when large accessories such as softboxes are fitted to the light. Some are air-damped or spring-loaded so if you lose your grip while raising or lowering the column the head's fall will be cushioned, protecting it from damage.
Useful for changing the colour of the light, either for creative purposes or to convert daylight to, say, tungsten.