Inasmuch as it’s useful, when editing an Ant build file, to have a list of the targets in the file and the ability to jump to any of them, my Ant mode at git@github.com:tkg/ant-mode.git currently only does two things: make a “Ant” menu that lists all the targets and associates a RELAX NG compact syntax schema with build files.
I had a more fully-featured Ant mode years ago but accidentally lost it when changing machines once, so putting the new mode on GitHub makes it both available to you and harder for me to lose. The motivation for reinventing it now came from from working with the build files in my fork of XML Calabash while I was adding the Ant task for running XML Calabash.
The current schema bundled with the mode is little more than a translation using Trang of the DTD dumped by <antstructure>, so I know I need to tweak it to make it easier to extend with custom task types, but in the meantime the mode is useful for when you’re looking at someone else’s build file (or your own when it’s grown big enough).