Guild Wars Nightfall

Campaign Three (a.k.a. Chapter Three) is an upcoming stand-alone product ("Campaign") of the Guild Wars game series, a follow-up of Guild Wars Factions (Campaign Two).

No title has been announced so far.

Content
Nothing is known about a theme or new content so far.

Release Date
No release date has been officially announced yet.

However, ANet hinted at the release date with two statements:
 * According to Jeff Strain Campaign III has been in development since Nov 2005 (source) and the development time for each campaign is roughly 1 year.
 * ANet have stated that they plan to release two campaigns per year, released on staggered six month cycles. Factions (campaign 2) was released April 28, 2006.

Based on this, the release date may be within a year from the time Factions comes out. But keep in mind that long-term target release dates in the gaming industry are often optimistic and tend to slip backwards.