Widgetbox
I have to make a special mention of this neat little tool called Widgetbox. It lets you easily create redistributable widgets for lots of custom sites like facebook, igoogle, etc apart from plain old HTML/flash widgets. I am leveraging it to send folks who use these widgets to landing pages within a web application via simple HTTP services in one of the projects that I am working on. Works like a charm and integrates quite nicely so props to the Widgetbox guys.