I've always found Cairnryan pier to be excellent, one of the guys in the tackle shop recommended it to me last year and I've never failed to catch on it. Of course the pier is now condemned and the port authority don't like you being on there, had a visit from the police once and they just ask you to leave, they even recommended a mark up the road to fish! The last time I was there the watchman patrolled on Monday, Wednesday and Fridays but it might of changed now.
You can catch all sorts off it, Thornback rays(need to whack it out though), conger eel down the side, cod, bass, flatties, coalies, pollack, dogfish and mackerel in the summer. I've even seen a guy pull up a big squid on daylights. Last time I was up a guy told me his son caught a small tope the other day too.
It's a good mark, but remeber it's still illegal to go on so it's at your own risk.