I've been using the serial library recently, and I've found an annoyance related to the Java type byte.

All numeric types in Java are signed, so the range of values for a byte is [-128, 127]. Mostly, when I'm reading serial data, I'd like unsigned information, and I think this is fairly common.

I propose that the Serial library should include functions for returning int[], similar to the readBytes() functions. Java represents bytes as 32bit values anyway, so there's no space saving to bytes. In fact, I suggest that the internal buffer should be int[] and another read function should be added:
Code:

public int read(int outgoing[]) 

I also wonder if a function to peek at incoming data would simplify some client code...
Code:

public int peek() {
  if (bufferIndex == bufferLast) return -1;
  synchronized (buffer) {
    return buffer[bufferIndex] & 0xff;
  }
} 

I'd be happy to donate an implementation, if there is interest.