A classic manga written and drawn by Masamune Shirow. Set in a cyberpunk-like future, it deals with the question of what life really means in a time when computers become intelligent, and humans can replace any part of their body, including the brain (wetware), thus asking Where's the difference?. Thus far, there have been two collections of this manga, the original part Ghost in the Shell, and the second part, Man-Machine Interface, which has so far only been published in japanese, with western editions pending.If there are new chapters currently published somewhere, I have not heard of them yet.
Maybe also of note: Both books have pages censored or replaced with new pages because of their more adult content (Cybersex et al).
Anyway, 1995 the first book was adapted to anime, directed by Mamoru Oshii and produced by Production I.G., which added some scenes while leaving others out. It is considered as one of the best anime ever in the west and the quality or animation set standards for years to come, also utilizing some computer-graphics, quite new at that time. Others in this node have already commented on the plot, so I'll leave it at that.
A movie based on the second book is currently in production, but not many informations are currently available. It seems that it will not be directed by Mamoru Oshii however.
Finally, another production has just recently premiered: Ghost in the shell: Stand Alone Complex, a state of the art 26 episode TV-series, directed by Kenji Kamiyama (Minipato) that is shown on Animax, a satellite pay channel since October. The music is provided by the ingenius Yoko Kanno. The US-rights have already been snagged by Bandai. More information under
http://www.production-ig.com/Ghost_TV.html