For the 2nd time today I am recommending this shop. Covert records in Brighton. Sound people who actually have memories, so when you go back to see them again they recommend stuff you will probably want to buy.
They're on-line now as well at
http://www.covert.uk.com

And I can't say enough good things about Innercity. Paul is a top bloke who always seems to recommend a couple of other gems whenever I phone in an order.

And Avid records for 2nd hand stuff of all genres. They've got a couple of stores around the country and now have a decent mailorder service as well. Can't find the url at the minute, but I'll post it when I find it.