Free XSLT Profiler
Today the XML Editor team released the XSLT Profiler Addin for VS 2008, a quick and reliable performance analysis profiler tool that assists in the development and debugging of XSLT documents. The XSLT Profiler allows developers to measure, evaluate, and target performance-related problems in XSLT code by creating detailed XSLT performance reports. The XSLT Profiler Addin for VS 2008 includes a wealth of useful hints for XSL and XSLT style sheet optimizations, which are essential for XSLT-based applications that demand maximum performance.
See a webcast demonstrating the tool here.