Since getting my Kindle, I've discovered the thousands+ of books available in DjVu
format, which the Kindle doesn't speak. Back in the day, DjVu had 1-2 orders of magnitude better compression for scanned documents than did PDFs, so it was used for many good books.
I have not seen this nice workflow for converting DjVu's into pdfs, so I'm reproducing it here. It uses Adobe Acrobat Pro 9, and produces pdfs with the same/better compression as the original scanned DjVu book, along with OCR searchable text. Looks fantastic on the Kindle 3.
1. Get djvulibre, djview, and djvu2pdf from sourceforge. On a Mac, this is simple if you have Xcode and Macports installed: just issue the command,
sudo port install djvulibre djview djvu2pdf
djvu2pdf file.djvu ; mv file.djvu.pdf file.pdf
3. Adobe Acrobat Pro: Acrobat>Save As...>Format: Adobe Files, optimized>Settings...>Make compatible with: Acrobat 9.0 and later>Save
4. Document>OCR Text Recognition>Recognize Text Using OCR...>Edit...>PDF Output Style>ClearScan
The optimized pdf is typically a little smaller than the original DjVu document, and OCR adds the benefits of searchable text, as well as rotating scanned pages and cleaning up the images a little.