I had the same type of thing awhile back, thought I needed to use a 555 and a pot to generate a variable freq output. I used a 12F675 and 2 buttons to make a nice square wave, one button increased freq, the other decrease freq. 8 pins, 1 pin power, 1 pin ground, internal oscillator, 2 pins for buttons, 4 pins left over, 2 pins at main freq (inverted from each other), the other 2 pins running at 1/2 and 1/4 of the main freq. Was able to adjust it from 0hz up to around 200khz. Worked like a champ, took the same amount of board space, and I suspect took less time to program that PIC than it would've to calculate the correct values for a 555 to get a 50% duty cycle square wave.

My 2 cents....
JDG