Argon

Argon does not react with the filament in a light bulb even under high temperatures, so is used in lighting and in other cases where diatomic nitrogen is an unsuitable (semi-)inert gas.
Argon is particularly important for the metal industry, being used as an inert gas shield in arc welding and cutting. Other uses include non-reactive blanket in the manufacture of titanium and other reactive elements and as a protective atmosphere for growing silicon and germanium crystals. Argon-39 has been used for a number of applications, primarily ice coring. It has also been used for ground water dating. Argon is also used in technical SCUBA diving to inflate the drysuit, due to its nonreactive, heat isolating effect.
Argon as the gap between the panes of glass provides better insulation because it is a poorer conductor of heat than ordinary air. The most exotic use of argon is in the tyre of luxury cars.