I’d start with the Data Collector. You can collect everything with Data Collector and then use the Log Parser and Visual Log Parser to help aggregate the data and even run queries against it. You may already know about some of these – but for those you haven’t seen, you should take a look!
Data Collector (supports IIS6 & IIS7, and can pull most other logs from any server):
http://blogs.msdn.com/b/carloc/archive/2010/02/01/idevdatacollector.aspx
Log Parser 2.2:
http://www.microsoft.com/downloads/en/details.aspx?FamilyID=890cd06b-abf8-4c25-91b2-f8d975cf8c07&displaylang=en
Visual Log Parser:
http://visuallogparser.codeplex.com/
Log File Analysis:
http://blogs.msdn.com/b/delay/archive/2007/06/21/powerful-log-file-analysis-for-everyone-releasing-textanalysistool-net.aspx
Event Log Explorer:
http://www.eventlogxp.com/
IIS Log Analyzer (does graphs and reports):
http://www.iis.net/community/default.aspx?tabid=34&g=6&i=1864
IIS Diagnostics Toolkit (a suite of tools diagnosing Authentication, Authorization, SSL, Crash/Hang, etc.):
http://www.microsoft.com/downloads/en/details.aspx?FamilyID=9bfa49bc-376b-4a54-95aa-73c9156706e7
and then of course the "big daddy" bunch of them all - Debugging Tools for Windows:
http://www.microsoft.com/whdc/devtools/debugging/default.mspx
I hope you find these useful : )