You need to be more specific mate, I could write a book on this. The important thing is not to try & cover too much in too short a time. Most of the beautiful scenery is over west which can be directly accessed by an international flight to Shannon Airport. The scenery south to Cork & north to Donegal is all stunning so we'd need to narrow your priorities down further and establish your time frame and the distances you want to cover.
Firstly we need to establish how much time you've got & what your main interests & draws are on this holiday, then I could draw you up a rough itinerary.
However on the east coast you have Dublin & south of that the beautiful garden county of Wicklow much of it covered by the Wicklow Mountains which are an extension of the Dublin Mountains. North of Dublin you have more flatland & the historical & archaelogical sites of the Boyne, Tara & Newgrange but if you're not specifically into that Wicklow IMHO has far more stunning scenery & should be more of a priority on your must see list.
In the south east you have the ancient city of Kilkenny with its stunning castle however its a more isolated atrraction since the surrounding countryside is charming, but not stunning.
If you're limited on time it may be best to stick either to the west or east of the country depending on your priorities. While the midlands do contain some gems much of the scenery is flat, uninteresting & if you're stuck for time not the priority IMHO. about 8 years ago