What's a 74HC165N do? Think of it as the reverse of the venerable 75HC595 - it's 8 bits in, serial out!
Where would you use a 74HC165? Imagine having to read 8 (or more - chaining is easy) digital inputs, and have an easy way to read them back to your microcontroller.
Hit the "Parallel Load" (PL) line with a LOW, and the digital state of the lines connected to D0 to D7 are read in. When PL is high, the data is serially clocked out of the chip. And fast too - it's able to clock at up to 29MHz!
This only takes 4-pins of your microcontroller, and there's even sample Arduino code.