My all time favorite analog oscillator is the Twin-T (the one with a BJT) [1]
It was hard to get a proper intuition of how and why it works, but when you finally do ... fireworks!
Another thing that's real fun with oscillators is to try and build a true chaotic oscillator, but only with R+C+BJT
Not easy, but can be done [2]
[1] https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj...
