CMOS Toggle Flip Flop With Relay(CD4013):

Discrete BiStable Flip Flop:

Discrete Set / Reset Flip Flop:

Flip-Flop Flashers, Buzzers, Etc.:

Gated Oscillator Emulates a Flip Flop: 03/16/95 EDN-Design Ideas 

MonoStable Flip Flops (One Shot):

Soft On / Off Switch: Modern electronic equipment incorporate "push-to-on-push-to-off" switches that do not make the clicking noise as with old equipment. An example of this is the power button on a ATX computer cabinet. Here is a circuit that does the same. It can be used to turn on/off any electronic/electrical equipment that operates on any range of voltages. FAIR WARNING -- THIS SITE HAS ANNOYING POP UP ADS.

Telephone Line Based Audio Muting & Light on Circuit: FAIR WARNING -- THIS SITE HAS ANNOYING POP UP ADS. 

Telephone Line Based Audio Muting & Light On Circuit: The circuit would automatically light a bulb on arrival of a telephone ring and simultaneously mute the music system/TV audio for the duration the telephone handset is off-hook. Lighting of the bulb would not only indicate an incoming call but also help in locating the telephone during darkness.