Hey hero,
Yep a small 8-pin micro was my first thought, and it will do the job nicely! PIC12F675, 629 just using comparators, and I have about 60 attiny15L's which have 100kHz PWM, internal osc, and ADC's. - Made for intelligent SMPS.
All the above would be better, but hey, I was thinking about something others could build, without being restricted to owning programming hardware/software. Nothing like a nice simple circuit which doesn't require any real special parts (everyone has a 555 somewhere). And yes, its efficiency isn't great, but at low currents, it doesn't really matter...this isn't for portable apps. As long as its PCB footprint is small and its super cheap. - no special IC's. Even a 1N4148 could be used for the diode at the cost of even lower efficiency.
I'm working on a 2/3 transistor version. Transistors are even easier for people to use, plus, designing a negative boost converter becomes easier.....just design a boost converter and switch the polarity of all polarised components. The Vout drops to Vout-Vin, but thats only 5v in my design.
I cannot think of any standard applications that require a negative voltage greater than -12V....for opamp bipolar power uspplies, I just use a max232 equiv. But it would be nice to have a small neat circuit which I can use for most of my 1/4VGA and 1/2VGA LCD's.