Here's a cool freebie that was recently mentioned on the Kindle 2.0 Blog--a set of star charts comprised of 14 PNG files and optimized for the Kindle. Created by Roban Hultman Kramer using PP3--Celestial Chart Generation software by Torsten Bronger, the images were designed to cover the entire sky, with significant overlap. As he explains on the page where the charts can be downloaded, "After my brother generously gave me an Amazon Kindle for my birthday, I started looking around the web for star charts that would be usable on it. The Kindle has an 600x800 pixel eInk display with four shades of gray. This means that most star charts meant for computer screens don't have enough contrast or are overly reliant on color, and most star charts meant to be printed require too high a resolution to be easily used on the Kindle. Compounding these problems is the Kindle's primitive image display interface, which doesn't allow scrolling of over-sized images."
After considering various planetarium programs for his charts, Roban found PP3 to be "perfect for this purpose." For more info, stargazers can check out this thread on the Amazon Kindle forum.