I have created two Facebook apps using del.icio.us feeds, Yahoo Pipes and the blidget tool offered by Widgetbox.
White Poppy promotes ideas for peaceful ways of living and images of peace. It also remembers with respect all those who have died in war, and seeks to bring an end to conflict so that such deaths might not happen in future. It is a mashup of two feeds: items tagged 'peace' on del.icio.us and items tagged 'peace' on flickr. Check out the official white poppy site. You can also buy a white poppy from various outlets.
MetaPagan is a Pagan and Heathen blog aggregator, to go with the Pagan community blog of the same name. It brings together blog posts by, about and for the Pagan community. You can contribute via del.icio.us.