Xenogears: Perfect Works is one of those often sought after artbooks by not only fans of the PS1 classic, but also by artbook collectors in general. This 303 page book not only contains art from Xenogears, but also provides an incredibly detailed background on the game's history, universe, and history that provides additional insight not revealed in the game itself. Xenogears: Perfect Works is also incredibly hard to find; the book has been out of print for a long time, and finding a good copy cost potential owner over $200 dollars.
Well, until now, anyway. Xenogears: Perfect Works is set to recieve a reprint in March, and is available for pre-order now at Fukkan for 5,250 yen (or about $50 or 37€). Fukkan can be a bit hard to navigate for non-Japanese speakers, but they do seem to ship to the U.S. and U.K. (although it's difficult to confirm). There's currently no word if other import sites will pick up the book for pre-orders.
It's important to note that this book is in Japanese, though it is still worth it for Xenogears fans to pick up without knowledge of the language. Also, there is a complete fan translation here.