K2pdfopt

K2pdfopt (Kindle 2 PDF Optimizer) is a stand-alone program which optimizes the format of PDF (or DJVU) files for viewing on small mobile reader and smartphone screens such as the Kindle's.  It is meant for text-based files on a white background which may also have graphics or figures.  It is fully automated and can batch-process PDF/DJVU files.

http://www.willus.com/k2pdfopt/