Why are they called flip-flops?
I had always assumed that it was just because they flipped states.  And flop may refer to the optional reset (causing the circuit to flop).  But, looking into a bit more ...

From the online etymology dictionary:

"Flip-flop in the general sense of "complete reversal of direction" dates from 1900; it began to be used in electronics in the 1930s in reference to switching circuits that alternate between two states. As a verb by 1897. Flop (n.) in the sense "a turn-round, especially in politics" is from 1880."

A flip flop is generally used to hold a binary value.  The "complete reversal of direction" is a good root (since a 0 vs 1 are opposites of one another).

Another illustrative general definition of flip flop: "To alternate back and forth between directly opposite opinions, ideas, or decisions."  This lends itself to binary representation well.  

So looks like the word existed before the electronic device.