If you use gimp there was a plugin written in 2008 called 'deskew'.
I got it running on my SLACKWARE 13.37 system and it is QUICK and ACCURATE.
Here is a before:
And AFTER: The canvas is showing through on the corners... and this was about 3 seconds of processing on a grayscale TIFF image
GIMP can be set up to batch the files and run without interaction