I keep getting asked by my customers what tools should they have handy so they can troubleshoot problems with IIS more quickly.

Having the tools locally provides the admins with the following benefits:

The ability to have a play with the tools before they are faced with a critical situation - i.e. They don't have time to learn how to use a new tool when the server is down etc
The tools have already been approved to be run on the production servers.
There is no hunting for the right tool or trying to get the tool from an internet site into what might a closed network

Here are a list of the most common tools Admins should be familiar with when working with IIS:

MPS reports http://support.microsoft.com/?kbid=818742

IIS Crash/Hang Agent & IIS Dump http://www.microsoft.com/downloads/details.aspx?FamilyID=01c4f89d-cc68-42ba-98d2-0c580437efcf&DisplayLang=en

ADSUTIL.VBS (this normally is located in the adminscripts folder under c:\inetpub but is sometimes removed

Log Parser 2.0 http://www.microsoft.com/downloads/details.aspx?displaylang=en&familyid=8cde4028-e247-45be-bab9-ac851fc166a4

Debugging tools and public symbol location

Windows Debugging Home http://www.microsoft.com/whdc/devtools/debugging/default.mspx

Install Debugging Tools for Windows 32-bit Version http://www.microsoft.com/whdc/devtools/debugging/installx86.mspx 
(Also includes ADPLUS.VBS)

Microsoft Baseline Security Analyzer V1.2.1 http://www.microsoft.com/technet/security/tools/mbsahome.mspx

MetaEdit download http://support.microsoft.com/default.aspx?scid=kb;en-us;301386

MetaEdit information http://support.microsoft.com/default.aspx?scid=kb;en-us;240225

IIS 6 resource kit http://www.microsoft.com/downloads/details.aspx?FamilyID=56fc92ee-a71a-4c73-b628-ade629c89499&DisplayLang=en

Let us not forget a good understanding of Network monitor and Performance monitor