EM Antiblock   
http://www.engelmann.com

By default, Microsoft Outlook will prevent you from opening certain file attachments that can damage your computer, e.g. by containing malware code. However, sometimes you need to be able to handle these attachments. EM Antiblock offers you the ability to easily decide which file attachments you can trust, by managing the file extensions for the blocked attachments. And the best of all: This software is freeware! Compatible with Outlook 2000 to 2003.

SharePoint Attachements   
http://www.kalmstrom.nu

Outlook can be configured to publish files directly to a SharePoint site instead of sending the file as an attachement. This allows you to make better use of your intranet and your Exchange server. Outlook is good for a lot of things, but not for file transfers. Works with any Frontpage or WebDAV site but of course best with SharePoint document libraries. Free 15 day trial and a low price tag of only 25 US$.

ADX Extensions for Outlook   
http://www.office-addins.com

The ADX Extensions for Microsoft Outlook allows you to customize the Outlook folder view and Outlook forms by embedding feature-rich .NET and VCL forms and controls into the Outlook Explorer and Outlook Inspector windows. The ADX Extensions for Outlook is based on the Outlook windows architecture and helps you create a custom Outlook folder view and custom Outlook forms in a more comfortable way than the Digital Dashboard technology (Outlook Today) or Windows API. Now you can use any .NET and VCL forms, controls and components (such as grids, editors and tree-views) on the Outlook Explorer and Outlook Inspector windows like form regions provides by Outlook 2007. The ADX Extensions for Outlook supports projects written on Visual Basic .NET, C# and Delphi in Visual Studio 2003, Visual Studio 2005, Borland Delphi 5 - 2006.