Family Tree DNA is holding their excellent Summer Sale. Some really good values there. If you want to research your family's history, locate your family that stayed in Ireland, etc., this is a great opportunity to do so.
For surname research the best test is the Y-DNA test. Only men carry the Y chromosome, so only men can do this test. The Y DNA will allow you to pinpoint your family's point of origin in Ireland, Scotland, etc., allow you to ascertain your paternal line's ethnic origin, to follow their migration path for thousands of years. You will locate cousins, confirm links, break through those infamous 'brick walls' that one encounters in family history research.
If you do not have access to a direct paternal descendant to test, there is another test of use; this is the autosomal DNA test, called the Family Finder test by Family Tree DNA. Women can use this test to locate a male from the line they are researching and then use his Y-DNA test. Men who are researching a line that comes through a maternal branch of their family can do the same. I successfully used the Family Finder autosomal test to locate a male from the line of my father's mother's family. It worked perfectly, I had a match to a female cousin and we had her brother test and in so doing obtained the Y-DNA of that line.
Links are below. If you are research and Irish family or family from the western Highlands or the Hebrides, do contact me if you need some help. That is my field of study.