Michael Dunn, a Senior Consultant for Microsoft developed an Add-In for Outlook 2007 which allows you to view and interact with your entire contact list from Office Communicator 2007.
This Add-In allows users to keep working in Outlook as well as view presence, call or instant message thier contacts. Outlook already gives you presence and functionality to communicate with the people for the currently selected email, but if you want to communicate with some one that isn’t included on the original email, you’d have to switch to Communicator. The idea behind this Add-In is that a lot of people spend the majority of their day in Outlook, so why do should you have to switch to another program to get presence and communicate with them?
The application with source code is available at http://code.msdn.microsoft.com/Communicator4Outlook
An other intresting Add-in for Outlook is Xobni. Xobni (Inbox spelled in reverse) is the Outlook plug-in that saves you time finding email conversations, contacts and attachments. It provides threaded conversations, Email analytics, personal assistant (for those who cant afford one) etc… Here is my outlook with both the plug-ins in action.