The new series is titled Darker Than Black: Ryūsei no Gemini. It’s set to air on October 2009! There are plenty of new characters, which can be viewed here. Among the characters, seiyū like Hōko Kuwashima, Hana Kanazawa and Mitsuki Saiga will be voicing them.
Moreover, there’s a PV streaming at the site, longer than the one streaming at the main page, you can watch them here by clicking on ‘1 M’. Aside from that, there’s a wallpaper for PC in three sizes. You can find them here.
Also, all the main staff of the previous series will return to work on the sequel. However, sadly, Yoko Kanno (my favourite composer! :D) will not be composing the music this time around… Instead, Yasushi Ishii will be responsible for it. How disappointing! *sighs*
Watch out for more updates!