From Ultimate-Guitar: "To record a piano, take a stereo pair of microphones (preferably condensers) spaced equally across the piano’s soundboard. For an upright, this will mean opening up the top and dipping them in to divide the piano into thirds with the mics being the dividers. For a grand, use the same technique across the much wider board. If you can hook up more mics, a grand can give you a gorgeous sound from all over. The point is to get a good stereo image of the piano. The range of pianos is such that you really should not attempt to do it with just one mic. If you have an electric piano or synth available, just take its headphone out or line out jack straight into your mixer."
