I've been using this - http://proto-pic.co.uk/breakout-board-for-electret-microphon
- to feed into my arduino. It's a bit noisy not great for low volume, but just about picks up speech at normal volumes and saves having to mess around with opamps yourself. If you were interested in trying an all software approach, I've had success using this FFT library - http://wiki.openmusiclabs.com/wiki/ArduinoFHT
if you use the electret breakout board, drive it from 3.3v and use the AREF pin on the arduino.
Also massively helpful is this - http://accrochages.drone.ws/en/node/90
- so you can see in realtime what it coming into the analog in. I was dicking around println'ing the outputs and drawing them in excel before I found it. Made it all so much easier!