Microsoft Exchange Server
http://blogs.technet.com/exchange/ Exchange blog
http://www.wlkmmas.org "Exchange Links and Stuff"
http://blogs.msdn.com/exchange/ You Had Me At EHLO...aka the Microsoft Exchange Team Blog
http://hellomate.typepad.com/ MS Exchange Blog

Spam
http://go.microsoft.com/?linkid=889756 Spam Do's and Don'ts
http://www.cluelessmailers.org/ I have not checked this out yet

Microsoft Outlook
http://www.lookoutsoft.com/Lookout/download.html Lookout is lightning-fast search for your email, files, and desktop integrated with Microsoft Outlook.  I have not tried this.
http://www.outlook-tips.net/index.html Looks promising, I have not tried this.

RSS "Really Simple Syndication"
Aggregators for MS Outlook
http://www.intraVnews.com/ - highly recommended (low cost or free)
http://rsspopper.blogspot.com/2004/10/home.html RSS Popper, free - needs a little work, but works fine for under 2000 news feeds. Do you read over 200 news sites? Not I!

Standalone apps
http://www.sharpreader.com/ (Sharpreader free) I used this for a while, but I want to move to intraVnews due to integration with Outlook.