Portuguese Wine reference
Amazingly, Richard Mayson's 2003 *The Wines and Vineyards of Portugal* appears to be out of print. Maybe an update is in the works? Don't know of a better book in English and have never seen a worthwhile French book devoted to the subject.
Edit: Amazon UK lets you view the book's table of contents, index and a few pages of text. www.amazon.co.uk/gp/product/184000733...
THERE AREN'T ANY!
My favorite remains The Wines and Vineyards of Portugal by Richard Mayson (2003 -- ISBN: 1840007338 . . . even though it IS out-of-print at the moment, you can still find it.
Other choices include:
Portuguese Table Wines by Giles MacDonogh (2006) -- ISBN: 1902304861
Jancis Robinson Tastes the Best Portuguese Table Wines by Jancis Robinson (1999) - ISBN: 972842373X
Both are out of date, as things are changing rapidly. Your best bet is magazine articles, such as in Decanter.