Handy dandy little circuit #23. Sine Wave Generators Square Wave Generators Logic Clocks and Oscillators Flashers To determine the resistance to be used for the LED current, substract 1.7v from supply voltage and divide by the current required in mA .
555 Timer Calculator. This page helps you calculate figure out the timing of a 555-based astable timer.
This page requires JavaScript 1.1 or newer. This circuit is the simplest. 555 triangle with independent slopes. View topic - CMOS 555 based square/tri VCO as LFO - how? Lostinpudy, yes I believe the control input should give you some frequency variability, though I have not looked at it and thought it through to be sure.
I'd go ahead and build it if you're a real fan of the 555. However, me, I'd choose the opamp circuit just cause I like opamps. Please do not let the -9V fool you!