If I was to stick to the rules stipulated by Darrman then Mountrath (Kilbricken), a particularly nice Sancton Wood station that's now sadly derelict.
If I were to stretch the rules a little, then Moate ( okay, a lot - but technically it still has rails through it), for the obvious reason that it would reinstate the Mullingar and Athlone link (not commercially viable, but I often thought it would make a nice heritage railway between two big towns - in which guise it might even happily co-exist with the greenway. It would need a very generous benefactor though)
If I were to continue that train of thought and throw the rules completely out the window, then Valentia Harbour .... reinstating that station means reinstating the whole line