Last time I checked, Airtricity charged exactly the same as the ESB, including the addition of a public service obligation levy charge. Their unit charges were the same, and the standing charges were the same. There was no benefit to changing over to Airtricity at all - apart from the environmental benefit obviously.
You could also try a company called Energia. I think they only supply business customers at the moment though. Although the electricity market in Ireland is fully-open to competition, the reality is that there are few, if any, alternatives to the ESB for domestic/residential customer. Perhaps the Commission for Energy Regulation could advise - www.cer.ie is the website.
Unless you are a commercial customer, forget about it. Unless you buy 4000 windmills and stick them in your back garden and blow like hell!! Energy competition is not for domestic users. Have you heard any ads recently offering cheaper electricity? Don't think so.