However, an equally interesting property of superconductors (from the point of view of a physicist) is their perfect diamagnetism and its limitation by magnetic flux penetration. And the most mysterious property of all is the phenomenon of macroscopic quantum interference as manifest in what I believe will ultimately prove the most useful of all superconducting devices: the superconducting quantum interference device or SQUID. This and its cousins offer the promise of quantum electronics using superconductors.
But we should not expect the money to start rolling in right away. Consider the example of transistors: from their invention: to their significant impact in the marketplace took nearly 30 years, and they were much easier to understand than superconductors!
Nevertheless, we are already starting to see some significant commercialization of the high-temperature superconductors discovered in 1987.
As of 1985, only a few materials were considered significant superconductors, and those were (not surprisingly) all metals. But in 1986 and 1987 everything changed with the discovery of copper oxide superconductors, which broke the liquid nitrogen barrier for the first time and made the 1900's the century of superconductivity.
One of the most glamorous proposed applications of superconductivity (and the one most often demonstrated publicly) is magnetic levitation (or "mag-lev") in which the ability of a superconductor to exclude magnetic flux (thereby producing repulsive forces between a magnet and the superconductor) is used to overcome the weight of an object (usually the magnet). These demonstrations work well with the cuprate superconductors because (a) they can be "turned on" with ordinary liquid nitrogen; and (b) these materials strongly "pin" magnetic field lines so that the magnet cannot easily "slide off" the top of the superconductor. The flux pinning has been found to be so strong in these materials that a magnet can also be suspended below a cold slab of YBa2Cu3O7. This discovery prompted the following tongue-in-cheek proposal: the "mag-sus" train. (I will not be the first passenger.)