The Web Address business type for Visual Studio LightSwitch 2011 allows validating Web addresses by checking if they are well-formed. This avoids the need of custom validation against strings that represents e.g. an URI, since validation rules are built-in the type.
This extension is part of the source code of my forthcoming book "Visual Studio LightSwitch Unleashed".
UPDATE: The extension now also offers a Viewer control that presents URLs under the form of hyperlinks and launches an instance of the browser for the given Web address.