Have you thought about using Silverlight for your SharePoint site navigation, or perhaps for a custom field control. What about a cool social networking Silverlight web part. Just announced at the SharePoint Conference is a Software plus Services blueprint which covers these types of scenarios.
It is early days, and so expect more content to be released soon. Have a look at http://www.ssblueprints.net/sharepoint/ for more information and links to various downloads.