I often go to the Barbican, specially on Mondays when all tickets are only £5. The movie selection is limited (only 2/3 screens) but they show decent movies. I went to see Mrs Henderson presents yesterday....
I use this link to find what's on at the movies:
I have just noticed that this week there is a film festival at the College Of Communication at the Elephant and Castle. It's all free and you can read more information on: http://www.newelephant.net/eleset.html
Now that I'm no longer entitled to student discounts, I don't bother with the West End cinemas any more - the ticket prices are truely shocking! I'd rather pay about the same or a little more and get a bargain ticket to a musical or play.
Peckham Multiplex (www.peckhamplex.com) at £3.99 a pop is the way to go if Peckham doesn't scare you too much. I'm sure only a year ago the tickets were £2.99, then went up to £3.50 in the summer. It's still very cheap though! And surprisingly the cinema isn't run down or unpleasent.
There's also Morrisons just behind the cinema for drinks and snacks if After Eight McFlurrys don't float your boat.