I save the original scans as BMP (no
compression).  You could also use a format that
uses lossless compression, like TIFF.  You don't
want to save your originals as JPG if you plan to
touch-up or resize them later, as JPG is lossy,
and you will get quality degredation if you save
it as JPG again after editing (and the original
will have degredation as well).  JPG is the format
you should only use as a final step.  (GIFs and
PNGs are other options for web graphics, but GIFs
only support 8-bit color, and PNGs cannot be
viewed in some browsers.)

--
Matt Martin -=- cels@nekomusume.net
http://cels.nekomusume.net/