"Dublinheritage.ie is a resource from Dublin City Public Libraries focusing primarily on databases derived from printed and other historic records related to Dublin city and surrounding administrative areas, " as stated on its website (http://www.dublinheritage.ie/). Several databases can be researched online for free on Dublinheritage.ie:

1. Community Memory. A database of all those named on commemorative plaques around the city - in churches, public institutions and open spaces.What is included? All those named on plaques, from large war memorials, to honour boards of presidents / officers of societies, family monuments, down to the single name on a kneeling board. 1950 was chosen as the cut-off date. Gravestones have been excluded and to date no house commemorative plaques have been included.To date 43 locations have been recorded, creating c.10,000 records. New records are being added on an ongoing basis.
2. Ancient Freemen of Dublin.  These records list all those admitted to the freedom of Dublin (i.e., citizenship and right to vote) during the period 1461 to 1491 and 1564 to 1777. Most Dubliners who became freemen did so by completing apprenticeship in one of the trade unions. The Local Government Act of 1898 enabled men over the age of 21 and women over the age of 30 to vote in local elections.
3. Dublin Graveyards Directory. This  directory covers all graveyards in the Dublin area (i.e., Dublin, Dun Laoghaire-Rathdown, Fingal, and South Dublin) and includes location, contact details, titles of published gravestone transcripts, links to online transcripts, etc.
4. Electoral Lists (1939-1940)
5. Electoral Lists (1908-1910)

In today's IrishRoots blog, John Grenham discusses the "extraordinary" value of electoral records, especially the newly-digitized records for 1908, 1909 and 1910. He states: The right to vote was vastly expanded in 1898 with the creation of an entirely new class of voter, the "inhabitant householder", who possessed no property, and so paid no property tax, merely having a stable address. This covered the vast standing army of Dublin's manual workers, surviving precariously, most of them occupying multi-family tenements. And here they are in these lists, living in the great belt of city-centre slums that arced around from East Wal, Monto and Gardiner Street through North King Street, over to the Liberties and down toward York Street to the Quays: household by household, room by room, year after year. Joyce's Dublin emerges vividly, stinking, dingy and overcrowded to a degree that is impossible to imagine now. The genesis of Dubliners and Ulysses becomes much clearer when you grasp the terrible, inescapable intimacy enforced by these teeming streets. Grenham explains that electoral records for 1911, 1912 and 1915 will be available online later this year. The project is part of Dublin City Council's 1916 commemoration so the full set of electoral lists will be available by April 2016. Note about Parish Records: The Database of Baptisms for Dublin Parishes, the Database of Marriages for Dublin Parishes, and the Database of Burials for Dublin Parishes, compiled by the Dublin Heritage Group for Dublin City Public Libraries, have been incorporated into the Irish Genealogy website. A description of the transcribed parish records and link to the Irish Genealogy website is provided by the library.