North west Donegal is best answer for you .

For the rocky coves bit, try the Waterford coast perhaps? Also slightly less buffeted by Atlantic/polar winds than Donegal or the northwest and very green. Also, it's full of nice little villages like Lismore, Stradbally and other places.

This isn't so useful for your coastline preference, but if you're driving around anyway I'd recommend the Midlands. For an interesting small town, there's Athlone, the home of Ireland's (maybe Europe's) oldest pub, Sean's Bar. 30 min south from there are the monastery ruins of Clonmacnoise, and another hour south is Birr Castle. And depending on where in the Midlands you stay, you could be in a prime star-gazing location. I stayed just outside of Longford town and I'd never seen the Milky Way so bright. However, staying in Longford meant that everything was a bit of a drive (~2 hrs to Dublin). Trains are more limited than they are along the east coast. But when the weather is good, driving the rural highways is beautiful and unbelievably green.
Edited by: lsalomon

Isalomon, Sorry my friend but Athlone (garrison towns are best avoided) is not a great town and Seáns bar is not the oldest bar in Ireland. The oldest bar in Ireland debate is ongoing? There are many that claim to be the oldest including "The Brazen Head" in Dublin which dates back to 1198. And certainly some of the so called oldest bars do not have the oldest interiors. In that respect check out Dick Macks in Dingle, Tigh Neactain in Galway and Hargadons in Sligo amongst many others.
The midlands for most of us who live in Ireland is quite flat and boring and lacking in culture to be quite honest! But hey if you enjoyed it then great stuff! Beauty is in the eye of the beholder, fair enough :)

stiofan, as an Athlone man, I can reassure you that Seans Bar is the oldest pub in Ireland at this time. Radiocarbon dating by TCD proves the mud-and-wattle structure of the building is centuries older than any of it's rivals. It has the Guinness Book of Records cert on the wall.
The Brazen Head is arguably the oldest NAME for a pub, but the building itself is a typical coach-house from the 18th century.
As for lacking in culture - oh dear oh dear oh dear. Should I start with the Corlea Trackway Visitor Centre, or Clonmacnoise, or any of the monastic settlements in Lough Ree? Sure, it's not on the beaten track followed by 90% of visitors, but you can't dismiss an entire region...
And BTW, as the brother, son, grandson, and great-grandson of professional soldiers, I feel offended that you advise visitors to avoid 'garrison towns'. Why? Do you think Athlone is full of drunken squaddies wandering around beating up unsuspecting tourists? I can assure you, any soldier coming to the attention of the Gardai would get very sharp treatment the next day in the barracks from his CO and it would be held against him if he wanted to re-enlist at the end of his contract.

Hi seaneendubh, Not saying it's members of the defence forces themselves, but I've done stints in Dundalk, Sligo and Newbridge and they all had the same problems. Athlone can be rough, I have been there plenty of times. I had a friend living adjacent to the castle and indeed Seans Bar but left for Galway to get to a decent social scene. Sorry Sean but I wont apologise on how I and countless more Irish people feel about garrison towns. We have a difference of opinion on this. Maybe different courses for different horses?
They have a different overall feel to them. Maybe this is down to history? (local people not to blame) Most of them were very much British Army towns before independence. So there is very much a class structured feel to them with I'm sorry to say a thug element today. I understand and respect your point on the Irish defence forces and Clonmacnoise is a good site indeed as is the river Shannon of course.