Recently, as part of Ancestry's 15th anniversary celebration, they gave access to Ireland's Griffith's Valuation. If you're not familiar with it, it was a valuation of property in Ireland overseen by Richard Griffin and published between 1847 and 1864. This valuation was the basis for determining the taxes paid by landowners. For genealogists and family historians, it offers an opportunity to locate Irish ancestors since all census records prior to 1901 were destroyed.
If you didn't get a chance to search this genealogy resource while Ancestry had it offered for free, it's not too late. I found another place that allows you to search it for free. Ask About Ireland has the index and images available. Searching the Griffith's Valuation is easy.
In step one, enter the surname of interest. There is an option to include similar names just below the box where you enter the surname. This is the only mandatory step. If you know the given name of your ancestor and where they were located, you can enter those in step two. Then hit the blue search button.
The results will give you a list of the occupier (who may or may not be the landowner), county and parish. You can click on the detail icon to get the landlord's name, more details on the location and information on the publication. To the right of the details icon is where you can view the original page.
Beside the original page icon, you have the option to get a map view of where your ancestors home was located. This is especially helpful for cases in which the name of the area or even street has changed over time.
If you find your ancestor and want to share some photos, documents or information about that person, the site has an option for that as well. Just click on the icon at the far right column on the results page. You do have to register with the site (appears to be free) in order to use this option.