How do I warp some interesting sounds out of my guitar without buying an FX pedal?

I've been messing around with noise just lately, such as picking a note then flicking the selector switch up and down to make a wah-wah sound. I've also been screwing about with the tone controls too, which creates some interesting feedback/spacey noises, and that violin sound (where you play a note then turn the volume control up).

What else can I do? I don't really "get" tremolos; apart from bending the strings and making them sound all detuned, what is the point of them?