A couple of weeks ago the Royal Irish Academy released a free pdf version of the Kilkenny edition of the Irish HIstoric Town Atlas (IHTA). (See blogpost here.)
If the IHTA is right up your street, you'll be interested in a tip I've received from Shane Wilson, who manages the swilson.info website (an excellent resource, especially, but not exclusively, for those researching Dublin families). Shane has found a few more free pdf texts from the Irish Historic Town Atlas tucked away in the Toponymy resources section of the Placenames Database website Logainm.ie.
While there are no separate maps available to view via that source, there are downloadable texts from Parts 1, 2, & 3 of the Dublin atlases and from the Tuam edition.