I thought I'd make a thread to recommend that HMV (I'm aware that on times I do sound like their PR gimp) have got a bundle of cult classics around the £2-£6 mark which is really worth exploiting.
I went in earlier today and picked up American Psycho and Kafka's Metamorphosis (&other stories) for £4 for the pair. Have also got Fahrenheit 451 and Brave New World from there before - they also have some Dickens, Verne, some others I'm too tired to remember.
Other than HMV - I tend to buy from The Works a lot. Their 3 for £5 deal