Back in May, I wrote an article for the Office Developer Center on MSDN on an idea I had for creating Outlook Calendar Providers (and later demonstrated how to write an additional provider for this to allow Windows XP Media Center 2004 recording schedules to be viewed as calendars in Outlook, which reminds me that I need to update that code for Media Center 2005). Since then, I've received several requests for code to do the same with contacts and contact lists instead of with events and event lists.
As it's the holiday season, I decided to spend a few minutes granting those requests and creating a version of the calendar providers code that instead works with contacts. For anyone who's interested, I'd suggest reading the article about calendar providers first, as the contacts code is very similar. The source for the new project is then available here. Included in the source is an example provider that connects to a SQL Server and provides a contact list for the customers in the Northwind database.
Of course, you can write your own providers to access whatever data source is of most interest to you.