I just finished up a 6 month internship with the Visit Dublin team in Failte Ireland. I was working on the www.VisitDublin.com website, which is the official tourism site for Dublin. Just before I left, the newly designed and updated Insider Guides went up. One of which is an Eco Dublin Guide which features lots of tips for vegetarian/Vegan dining in Dublin. I was happy to see such a useful resource being implemented.
You can download the handy guide here. And check out the rest of the guides too, they're great.