If you have to research Irish Ancestry you are better joining one of the Irish Family History Societies:
http://www.censusfinder.com/irish-family-histo ry-society.htm
the reason for this is not just to find what sources have been tranbscribed ot indexed, but also to tap into the wealth of knowledge and experience being with a FHS brings.
I also agree that ancestry.co,uk is the best site but u can use the library edition free in your local reference library and look at the GRO index to birth death and marriage 1837 -1984+ and all the census returns 1841-1901, all for free, you can also join their support groups there too.
I always recommend using the free version at the library first if you can get there, as it gives you time to work out how the index works and also it means you are not paying to learn how to use the site and the records.