Sun Application Server
The Sun Java System Application Server is part of the Solaris Enterprise System. You can download it now and use this sophisticated infrastructure software at no cost. And, if you need assurance and support, Sun offers licensing and support plans for purchase.
JBoss Application Server
JBoss Application Server is the #1 most widely used Java application server on the market. A J2EE certified platform for developing and deploying enterprise Java applications, Web applications, and Portals, JBoss Application Server provides the full range of J2EE 1.4 features as well as extended enterprise services including clustering, caching, and persistence. More
Oracle Application Server 10g Java Edition
Oracle Application Server 10g Java Edition is a highly scalable, available, manageable and secure J2EE application server that includes all you need to develop and deploy enterprise Java applications at a fraction of the cost of BEA or IBM. More
The application and transaction infrastructure delivers high-volume transaction processing for customers mission-critical applications, through two application enviroments with excellent security, and built on the latest technolgies such as Web services standards. More