Below is a directory of websites and resources related to Java Performance issues.
 

Books

"Java Platform Performance: Strategies and Tactics" by Steve Wilson & Jeff Kesselman
The book and related resources are available online at http://java.sun.com/docs/books/performance/ .

"Inside the Virtual Machine" by Bill Venners
Sample chapters of the book are available online at http://artima.com/insidejvm/ed2/index.html .

"Performant Java programmieren" by Hendrik Schreiber
Additional information (errata, links, downloads) can be found at http://www.tagtraum.com/performance/ .

"Garbage Collection" byRichard Jones & Rafael Lins
An excellent book on garbage collection algorithms in general; more information at http://www.cs.kent.ac.uk/people/staff/rej/gc.html .

Links & Resources

Sun Microsystems
A collection of links and resources at Sun Microsystems can be found at http://java.sun.com/docs/performance/ .

Jack Shirazi
Further resources for Java performance tuning including a list of tools can be found at http://www.javaperformancetuning.com/resources.shtml .

Articles, Papers & Specifications

JSR-163: Java Platform Profiling Architecture
The profiling architecture as designed for release in J2SE 5.0.  The specification group's page can be found at http://jcp.org/en/jsr/detail?id=163 .

WHITE PAPER: J2SE 5.0 Performance White Paper
The paper gives an overview of the performance and scalability improvements made in the J2SE 5.0 release along with various benchmarks to demonstrate the impact of these improvements. It has numerous links to further resources.