Wansdyke Project 21 (http://www.wansdyke21.org.uk/) -- A project to preserve Wansdyke (the earthwork). Includes a FAQ (http://www.wansdyke21.org.uk/faqs.htm).
Vortigern Studies is an initiative based in the Netherlands, dedicated to the study of the period between the Roman occupation of Britain and the Early Middle Ages.
"Wansdyke Project 21, which is launched through this website, has the aim to support the preservation of the ancient monument known as Wansdyke.
Wansdyke Project 21 aims to endorse this by making it better known to the general public by discussing all aspects of this unique Dark Ages earthwork."