1-wire parasitically powered microcontroller?
The one wire bus has the bus passively (i.e. with a resistor) pulled up in the system, and devices communicate on the bus by pulling the bus down. What I would do if I wanted to pull power from the bus is:


Feed the data line right into the
data input pin of your
microcontroller. 
Also feed the data
line into a Schottky diode. 
At the output of
    the diode put a largish (say 10uF)
    capacitor to ground.  
Send the
        output of the diode to the VCC pin
        of your microcontroller.


You should use a Schottky diode, to minimize the voltage drop. The diode/capacitor combination should make it so that communication can take place (i.e. grounding the bus periodically) without shutting down the MCU. Putting the capacitor after the diode will keep the transitions on the bus data sharp, while keeping the decay of power (voltage) to your MCU gradual. The lower power the device you use is the better to minimize drain on your capacitor, but pretty much any MCU will probably work for you. My preference is Atmel's AVRs, but TI MSP430s and Microchip's PICs are also good candidates for low power consumption.