The greatest thing since...

July 7th, 1928: sliced bread was sold for the first time in Chillicothe, Missouri by the Chillicothe Baking Company. The Rohwedder bread slicer holds U.S. Patent 1,867,377 and the Google Patent Search page has some a pretty nifty PDF of original sketches. Interestingly, sliced bread was banned briefly in the 1940s as a conservation measure during World War II. Madness ensued among American housewives and the ban was quickly lifted after three months' time.

And to answer the question that has been long burning in your mind, the greatest thing before sliced bread was apparently wrapped bread-- the Chillicothe company advertised their new sliced bread with the line "the greatest forward step in the baking industry since bread was wrapped."