Pelican cases are bomb-proof and some of the larger ones come with foam that you can 'pick out' to size and shape to hug the contents.
http://www.pelican.com
Otterboxes do a similar range but I think are not quite as sturdy. However, for all intents and purposes such as putting the Cybook at the bottom of a bag or backpack they do the same sterling job.
Tom Bihn does a range of portfolios and packing bags and cubes:
http://www.tombinh.com Excellent quality.
Finally, the local stationery shop sold me a nice A5 padded case that was just the right size for my HP iPaq Enterprise 214. You should be able to find something similar in your area.
Regards,
Ian Thomas (waiting with pleasurable excitement for the delivery of his Cybook)