me me i know!
well, its not all keyboard but i use this when making my pixart - click mouse, hold shift and drag - voila!
you can also join up points easily by click ng on one point then moving mouse to the other point, hold shift and click - voila
also if you click down on the rectangular marquee button, a line one comes up - very useful for:
drawing straight lines
counting how many pixels in a line (trust me, so hard without it)