Make sure you hire a car when you get over here, public transport dosn't always suit a photographers needs
If you could get down to the Burren in the south west, there's some fantastic spots there. Most of the coast is great. Pop over to the Islands if you're in Galway. Donegal is a fantastic spot, if I were you, I'd head straight up the Inishowen peninsula, there's a great fort up there, along with plenty of barely discovered spots. A trip over to Derry would be worthwhile too.
As mentioned, plenty of film. If you're flying in to Dublin, check out Gunn's camera shop, they'll have a good stock of film, if you want to avoid the dreaded x-rays. Also, if you'll be in Dublin, while not nessicarily photographic, there's plenty of exhibitions around which could be worth checking out, the Irish Museum of Modern Art being one of the bigger ones, and there's the Gallery of Photography in Temple Bar.