Java EE 6 (JSR 316) is arriving quickly (Q1 2009). With most of the specifications, comes a TcK (Technology Compatibility Kit) and a reference implementation (RI). Here is the list of the main reference implementations :
.GlassFish V3 is the reference implementation for EJB 3.1 and Servlet 3.0
.EclipseLink : Java Persistence API (JPA 2.0)
.Jersey : Reference Implementation for building RESTful Web services (JAX-RS 1.0)
.Metro : Web Services (JAX-WS 2.2)
.JBoss Seam for Web Beans 1.0
.Mojarra for JSF 2.0