Sun Java System Message Queue

Sun Java System Message Queue is a premier Java Message Service (JMS) implementation and is a leading business integration enterprise message server. An affordable, standards-based (JMS) messaging solution, it delivers superior return on IT assets by connecting business software together to form one efficient enterprise.

http://www.sun.com/software/products/message_queue/index.xml

Apache ActiveMQ

Apache ActiveMQ is the most popular and powerful open source Message Broker. Apache ActiveMQ is fast, supports many Cross Language Clients and Protocols and many advanced features while fully supporting JMS 1.1 and J2EE 1.4.

http://www.openldap.org

IBM WebSphere® MQ

IBM WebSphere® MQ delivers reliable application integration for applications and Web services, allowing you to fully leverage your existing software and hardware investments.

http://activemq.apache.org