Here is the definition of the peek function from the Serial Lib:
Returns the next byte (character) of incoming serial data without removing it from the internal serial buffer. That is, successive calls to peek() will return the same character, as will the next call to read(). peek() inherits from the Stream utility class.
This is the functionality that I'm looking for in NewSoftSerial (now called SoftSerial in Arduino 1.0).
Thanks!