IATE
IATE (Inter-Active Terminology for Europe) is the European Commission’s new multilingual terminological databank and replaces the earlier tool, Eurodicautom. This language site currently enables users to find translations for 1.4 million terms in 24 European languages, including English and Irish.
http://iate.europa.eu/iatediff/

English-Irish Dictionary
This website offers a free online dictionary with translations of words from English to Irish. It contains over 26,000 words translated and put to use as well as 1,400 English and 768 Irish verbs conjugated and translated.
http://www.englishirishdictionary.com/

Dicts
This English-Irish dictionary translates words from both languages instantly, and allows the user to type in just part of a word to find all possible matches. The site also features a picture dictionary.
http://dicts.info/ud.php?l1=Irish&l2=