Microsoft Performance Guidelines
Microsoft has a list of documents containing interesting tips and customizations that can be performed to improve or get the maximum performance of your operating systems.
For example, the document Performance Tuning Guidelines for Windows Server 2008 R2 contains more than 90 pages with tips and shopping information and technologies for Hyper-V, files servers, database servers, SAP, etc. They are both for Windows 7 and Windows 2008 R2.
In addition to this document for those using Windows Vista or Windows 2008 (without the R2) use the document Performance Tuning Guidelines for Windows Server 2008 containing more than 80 pages with the same content from the previous one.
To see all documents go http://www.microsoft.com/whdc/system/sysperf/default.mspx.