AIP4WIN Astronomical Image Processing for Windows is an excellent book by Richard Berry et al that also includes AIP4WIN a powerful astronomical image processing program. The book is available from Willmann Bell for $79US. http://www.willbell.com/aip/index.htm
Astroart A complete software for 96bit image processing, photometry, astrometry, CCD and DSLR control and image stacking for CCD and film images. http://www.msb-astroart.com/default.htm
Astrostack AstroStack, a freeware astronomical image-processing program, will do dark subtraction and stacking and other functions all at once and is a good way to get started with image processing. To use this program the images must first be converted to BMP format and reduced in size by either cropping or resizing. http://utopia.ision.nl/users/rjstek/english/software/index.htm
Cadet Cadet, another freeware astronomical image-processing program, is more complex but provides advanced functionality not found in other freeware programs. To use this program images must be also be converted to BMP and then colored images split into their red, green, blue, and optionally luminosity components. http://www.terra.es/personal2/oscarcj/introeng.htm
ImagesPlus Very pwerful and reasonably priced image processing software. Will load JPGs directly and work on them without having to split into RGB. http://www.mlunsold.com/
Iris Iris, also free, is an astronomical image-processing program with a command line interface that can be saved as a script for batch processing. This software is by Christian Buil. http://www.astrosurf.com/buil/us/iris/iris.htm
Paint Shop Pro Paint Shop Pro, an inexpensive but powerful general graphics program with a 30-day trial, which has many advanced features including Arithmetic options, which are perfect for Color dark subtractions of Digital Camera images. http://www.jasc.com/products/psp/
Quick and Free Dark Frame Subtraction Free software to perform dark fram subtraction, check out the other software too! http://www.mediachance.com/digicam/blackframe.htm
astRaw astRaw is a free (and open sources) tool for building a pre-processed image from acquisition of raw CCD images. http://elynx.sourceforge.net/astRaw/