Corsets have recently seen a resurgence in popularity, first driven by the movie Moulin Rouge and most recently, by the increased interest in Steampunk fashion. This site attempts to chart the details of modern day corsets and the various cultures and sub-cultures that use it today.
Corsets have, over the past 100 years seen brief resurgences after they last mainstream decline in 1920. In the 1950's and 60's, a waist cincher called the 'waspie' was introduced but soon fell out of fashion as Christian Dior's New Look fell out of fashion. In the 1980's, brief revivals occurred due to the release of the movie Moulin Rouge and the introduction of more period movies during this period. In the last decade, the increased interest in Steampunk fashion has seen a quieter, and potentially more lasting, revival of the fashion.
Of course corsets haven't ever gone completely out of sale. The BDSM and goth community embraced the corset, though instead of wearing them on the inside underneath clothing, the pieces were worn on the outside. And of course the re-enactors (Society of Creative Anarchorism) and otherwise have always worn it as an article of clothing, depending on the period.