You'll have to get Frommer's guide for Ireland. It lists all the great things to see (and Ireland is full of them). The Cliffs of Moher (pronounced Mow-her) are an absolute must. And the castles with meals and a show, although done specifically for us tourists, are FANTASTIC.
Quick Tips:
Rent the smallest car you can get and make sure it has an automatic transmission. Most rental cars in Ireland are stick shift. But remember, you'll be driving from the right side of the car and on the left side of the road - both exactly opposite from the US. And the roads are EXTREMELY NARROW. Many cars are missing side mirrors from hitting the stone fences that are inches from your car when you’re driving. Although you may be offered a much larger car for far less money, which has a standard (stick shift) transmission, DON'T TAKE IT! After you've been there a few times you can see if you think you're up to it but to have an enjoyable trip, go with a SMALL AUTOMATIC rental car - this is my BEST TIP!!Best Way To Get Around:
We rented to cars and a cottage for the week. It was great. A group that wanted to go to Dublin for a day drove one car up to a bus station and took the bus round day trip to Dublin. Although they were glad they went, they said Dublin is just like our big cities now (New York, Chicago, etc.) but the bus trip was really nice because driving yourself can be a bit nerve racking.