Argon is the most common noble gas on Earth. It is has a wide variety of uses due to its low reactivity.
Praxair (NYSE: PX) - http://www.praxair.com/ - manufacture argon commercially using air separation technology.
Airgas (NYSE: ARG) - http://www.airgas.com/ - also produces argon with cryogenic air separation. Liquefaction and distillation produce a low-purity crude argon which is then purified to commercial specifications.
Air Products (NYSE: APD) - http://www.airproducts.com/