Establishing Baselines & Benchmarks When you are hired as a DBA in a new shop, what are the important tools that you would use for establishing baselines and implementing benchmarks for 50+ instances? You advice would be highly appreciated.
For Microsoft SQL Server, the lowest-intrusive tool is Performance Monitor, aka Perfmon.  Here's my tutorial on grabbing Perfmon counters for SQL Server and analyzing them:

http://www.brentozar.com/archive/2006/12/dba-101-using-perfmon-for-sql-performance-tuning/