What is the simplest way to make an oscillating signal?
Lowest component count I can think of:  



The 74HC1G14 is the single gate version of the 74HC14 in SOT-23 package.  

OK, I lied. You can do it with less. Take a microcontroller with an internal oscillator and write this incredibly complicated program to output a square wave. Number of components: 1. Board space: 6 mm\$^2\$.  

If you drop the frequency restriction you can use a LED: f ~ 374740572500000 Hz. ;-)

Also out-of-spec is the Schmitt-trigger inverter with the output connected to the input. That's also a 1-component solution. Should oscillate at a few MHz.