What are some software add-on's for Microsoft Outlook?

Two software packages I really like for Microsoft Outlook are Lookout and Attensa. Lookout is a search toolbar that quickly indexes your email messages, attachments, folders, and other Outlook files. Because it pre-indexes all files, search results are returned in seconds. Lookout is a free download for Outlook 2000 and later.
http://www.lookoutsoft.com/Lookout/download.html

Attensa is a simple add-on which delivers RSS feeds into simple, easy email messages. Attensa is a RSS reader that adds on to Outlook. Attensa is $30 and is available at:
http://www.attensa.com/