New updates and patches. It also includes the previous SPs so if you haven't installed SP2, just go straight to SP3. Here's the link to Microsoft to find it.
Formerly code-named "Titanium" Microsoft's next version of Exchange is expected to ship in the middle of this year. For more information: http://www.microsoft.com/exchange/evaluation/ti/default.asp
Have an Outlook question? It might be answered in my Microsoft Outlook FAQ.
Somorita Surfboards -- I know, strange name, but good Exchange resources.
The best site I know for Exchange Server, and particularly Microsoft Outlook, information, is Slipstick Systems. Funny name, but lots of great information.
CDOLIVE - Siegfried Weber's outstanding site on Exchange programming. A must read for anybody planning to develop for Outlook.
Microsoft provides a good Exchange Server site as you would expect.