RuggedCircuits:
Well, you can start with this idea:http://ruggedcircuits.com/html/circuit__2.html
Now, the details are going to be important when working with signals as low as 55mV and down. How much resolution do you need? How careful have you been with noise or is the noise arriving at your op-amp inputs going to swamp your 55mV signal?
The TLV2731 op-amp suggested in the circuit above is inexpensive, but its error specifications (e.g., offset error) are magnified by gain. If you try to boost the 55mV signal to the full 5V range (gain of 91) then the offset error (typically 5mV or less) is also multiplied by 91 (455mV). So your signal may end up in the range 0V to 5V but no have ~0.5V of uncertainty in it, just due to op-amp noise.
What I'm getting at is: what's your application? How important is precision and noise? etc. etc. There are certainly better choices than the TLV2731 (for more $$$) but it's not worth it if it's not necessary.
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The Gadget Shield: accelerometer, RGB LED, IR transmit/receive, speaker, microphone, light sensor, potentiometer, pushbuttons
now this is helpful. I'm going to digest all of this and reply. Thanks RuggedCircuits.