pynemap is a script to generate map images for Minecraft, suitable for
cronjobs or whatever. Apparently works on Windows and OS X. I try to keep
compatibility with different OSs and Python2.4 but no promises.
Usage is:
./pynemap.py: [options] path/to/world/level.dat
    General Options:
        -o|--output-file <filename>
            The filename of the resulting image. Should end with ".png"
            default: map.png
        -r|--render-mode <['overhead']>
            The method for rendering the map image
            default: overhead
        -v|--verbose
            Output progress and other messages
            default: off (quiet)
        --processes <count>
            Set the number of render processes
            default: # of cpu cores

Note that it requires having the Python Imaging Library (http://www.pythonware.com/products/pil/)
(probably installed by default on most distros) and progressbar package
(http://pypi.python.org/pypi/progressbar/) installed already.

Thanks to Cartograph for the block colors and tWoolie for the NBT parser (viewtopic.php?f=25&t=24585)!
Thanks to various people on minecraftforum.net for help with the coding and whatnot!

Examples of render-modes:
blocks: don't have one yet
oblique: http://waysaboutstuff.com/oblique-example.png
overhead: http://waysaboutstuff.com/overhead-example.png

Current release version: release-0.1b2