I've noticed a lot of these events popping up lately. I used to go to the Odeon on Thursdays for their free classic movie nights. It's worth it as you can have your pint and a bowl of chips for under a tenner and sit in comfort all night while people bring you anything you need.
Happiness. So the Grand Social bar are also doing classic movies, but on a Tuesday so you can do both! If you check the websites, the Odeon require you book in advance and both theme their movie nights. The Odeon are currently doing a Clint Eastwood theme and Grand Social are going with Sci Fi.