amplifying mic signals in an arduino

Using Arduino Audio
5

You might consider buying an op-amp breakout board like this one for $5:

SparkFun OpAmp Breakout - LMV358 - BOB-09816 - SparkFun Electronics?

Or even better here is a breakout board with a Mic and a built-in amplifier for $8:

I used the latter successfully in an Arduino project that took Mic input, applied a ring modulator effect, and then played the output on a speaker. Here is a link with circuit diagrams and code:

Hope that helps.