For months, it seemed that after the county was upgraded to a special municipality, it would be known to the outside world as Xinbei City, a direct romanisation of its Chinese name (新北市, literally 'New North City'). That's why I used Xinbei in the first edition of my guidebook. Fortunately, this shouldn't cause problems for visitors, as they'll be boarding buses and trains to places within New Taipei City such as Danshui, Wulai and Sanxia (pictured left).
I feel better knowing I wasn't the only one caught out. The new edition of The Handy Guide for Foreigners in Taiwan (published by the central government in November 2010, but I've only just received my copy) says that the new name of Taipei County will be Xinbei City.