A commercial high quality balanced microphone preamplifier.
http://www.rane.com/pdf/ms1bsch.pdf
based on SSM-2017 IC
http://margo.student.utwente.nl/el/analog/micpre.gif
It has an exceptionally fast high frequency response, as demonstrated by applying an 100kHz squarewave to the input.
http://www.zen22142.zen.co.uk/Circuits/Audio/gmpre.htm
The preamp can also be used with other amplifiers, and can drive an impedance of 2k Ohms with ease.
http://sound.westhost.com/project37.htm
A low voltage preamplifier optimised for 3 Volt operation.
http://www.zen22142.zen.co.uk/Circuits/Audio/lvpreamp.htm
Preamplifier circuit
http://www.electronics.50g.com/cpowers.htm
This preamp is very simple, and will work under tough conditions. The input impedance is pretty high, so it won't load down electric guitars.
http://www.bobblick.com/techref/projects/preamp/preamp.html
None of the parts are critical. Use whatever you have. Again, note that the microphone is a "electret" type.
http://www.uoguelph.ca/~antoon/circ/amp1.htm
A very convenient way of making an intercom is to use a loudspeaker as a microphone. This is a preamp with a low input impedance suitable for this purpose.
http://www.4qdtec.com/preamp.html
While the voltage off an electromagnetic guitar pickup can be a healthy 2.0 Volts or so peak-to-peak if you're playing hard, the impedance of that signal varies greatly over the frequency spectrum and a high impedance signal can be damaged interfacing to the outside world.
http://www.till.com/articles/PreampCable/