With the Java EE 7 release date getting closer and closer, this is a great time to download the promoted versions of GlassFish and start experimenting with the new APIs. Most of the Java EE 7 APIs have been at least partially integrated already. The URL to get the promoted builds is: http://download.java.net/glassfish/4.0/promoted/. Don't get too overwhelmed by the directory - besides every promoted GlassFish zip, it also has artifacts like the Java EE APIs, Javadocs, UNIX and Windows installers, web profile bundles, etc. The latest version of each artifact has the naming pattern 'latest-*', so the latest GlassFish zip is at: download.java.net/glassfish/4.0/promoted/latest-glassfish.zip. You should be able to use either NetBeans or Eclipse.
Besides the promoted builds, the nightly builds are available at this URL: download.java.net/glassfish/4.0/nightly. Happy hacking! Drop me a note if you need help...