Kodansha has launched a portal centered on XXXHOLiC: http://kc.kodansha.co.jp/SEP/02888/01/xxxholic_portal/
The site so far seems to gather all the news and information about the current XXXHOLiC-related products and developments like the artbook release, the new manga series, TV Drama adaptation and the XXXHOLiC Cafe.
You can also see a very large version of the artbook cover. This page says that the artbook will come with 3 new illustrations drawn by CLAMP.
2013 is definitely going to be XXXHOLiC's year.