Eoin from www.irishdictionary.org works hard to bring Irish language resources to as many people as possible, for free.
His English Irish dictionary online is a great example of this.
It's a wikidictionary - created by submissions from its users. The dictionary has over 1,500 entries, and it's growing every day. You can also download a pdf containing all the dictionary entries.
Eoin's aim is to have a simple, accessible dictionary with fast search. You can search in Irish and in English. Eoin himself is the first to admit his dictionary isn't perfect - but it's better to have something than nothing.
Eoin's approach and goals can be summed up in two old Irish proverbs:
Tús maith, leath na hoibre - A good start is half the work
and
Trí na chéile a thógtar na cáisléain - In our togetherness, castles are built.
Is fearr dhá theanga ná ceann amháin…