Time to dig out some favourites from my browser and share the top Exchange admin tools / sites …
Mailbox Server Role Requirements Calculator – Helps you properly design Mailbox servers for your environment,
http://blogs.technet.com/b/exchange/archive/2009/11/09/3408737.aspx
Exchange Remote Connectivity Analyzer (ExRCA) – Provides a test system for administrators to use to validate external connectivity to Exchange. Essential for testing your activesync / autodiscover deployments !
https://www.TestExchangeConnectivity.com
Microsoft Active Directory Topology Mapper – Reads Active Directory configuration using LDAP, and automatically generates a Visio diagram of your Active Directory and/or Exchange topology,
http://www.microsoft.com/en-us/download/details.aspx?displaylang=en&id=13380
Exchange Server Deployment Assistant (ExDeploy) – Generates custom instructions for moving your organization to Exchange 2010 or Office 365,
http://technet.microsoft.com/en-us/exchange/jj657516
Exchange Client Network Bandwidth Calculator – Helps you predict network bandwidth requirements for a specific set of clients,
http://gallery.technet.microsoft.com/Exchange-Client-Network-8af1bf00
I know I said 5, but this one is too good to ignore !…
Microsoft Active Directory Topology Mapper – Reads Active Directory configuration using LDAP, and automatically generates a Visio diagram of your Active Directory and/or Exchange topology,
http://www.microsoft.com/en-us/download/details.aspx?displaylang=en&id=13380