These "Lite Cylinders" are made from fiberglass, making them both easier to toss around and safer. Unlike standard propane tanks, the Lite Cylinders won't corrode, are translucent making checking gas levels easy, and don't explode when exposed to fire. (Or so they claim. It'd be fun to prove them wrong.)
Unlike the steel tanks you can rent from the hardware store, the Lite Cylinders are $100 a pop.
A Propane Tank With a Clear Difference [Toolmonger]