I've done a fresh download and extraction of the latest Helios Eclipse and then installed the latest Jboss tools through Install Software -> http://download.jboss.org/jbosstools/updates/helios/
What I noticed was that the content assist (ctrl space) does not work for most tags - (a4j, seam, core and many others) on xhtml files, the only one it works for is the ui tags.I installed JBossAS Tools, Seam Tools, JBoss Tools Rich Faces.
I replicated the exact same steps on ganymede and it works out of the box! Are there additional steps required in the helios version or is there a bug?
Thanks for your time in reading this.