This depends on what type of music you are recording.
For something along the lines of "classical", I would suggest two large diaphragm condenser microphones. Place one microphone a few inches from the hammers, near C2. Place the other microphone near the back of the piano, centered over the copper bass strings. Both mics should be 6-12 inches above the strings, depending on the sound you want. Close will have less "room" sound. When mixing, pan the left mic slightly right, and the right mic slightly left. This will recreate the image of listening to the piano from an audience perspective.
If the music is rock, you have more options. For the piano to really stand out in a mix with other instruments, I like to use a stereo pair of small diaphragm condesers (two sm-57s are acceptable also). Place the mics in an X configuration aboud 1' above the strings, near the hammers. This will capture the percussive sound of the piano and let it cut into the mix. Pan left hard left and right hard right. The other option, if the piano plays more of a rhythmic role, is to record in mono and pan center.
For Jazz, one or two large diaphram condensors generally work well, quite close to the strings (5 inches). This can give you a very warm, yet bright sound. Make sure the microphones you use can handle the high sound pressure levels at this distance, a piano can generate huge amounds of sound pressure.
As for microphone choices, if you are on a budget you might want to look at some of the budget condensers, like Behringer of MXL. I have heard great things about the Studio Projects microphones also. Make sure you have a preamp that provides phantom power, which these microphones require.
If you chose the SM57, which I would only recommend for Rock, you will not need phantom power.
Hope this helps.
YM