Back in August 2010 The Irish Family History Foundation’s Online Research Service (ORS) announced the availability of the census records for 1901 for Limerick and Dublin South. http://ifhf.rootsireland.ie/ They now have over 1.8 million census records searchable online. These will shortly be added to the Central (All Ireland) Search.
Do check them out as there is lots of useful data here. You can also view Irish Ships Passenger lists.