The IBM Extensions for Memory Analyzer (IEMA) are a set of free plugins that extend the powerful Memory Analyzer Tool with product-specific knowledge when analyzing heapdumps and system dumps. For example, IEMA can list out all HTTP sessions, attributes such as their JSESSIONIDs and user names, and session attributes in a nice tree view for WAS dumps (note that much of the additional information is only available with system dumps on IBM JVMs). For more information on WAS-related extensions in IEMA, see http://www.ibm.com/developerworks/websphere/techjournal/1103_supauth/1103_supauth.html.
Previously, IEMA was a bit difficult to install. Now, however, the extensions are available as tool add-ons in IBM Support Assistant: http://www-01.ibm.com/support/docview.wss?uid=swg21512317. In ISA, go to Update > Find New... > Tools Add-ons, and select the IEMA plugins from the JVM-based Tools (of course, you'll also need IBM Monitoring and Diagnostic Tools for Java - Memory Analyzer).