Buy/Sell/Trade would be a good starting point - at least you would know that items probably went to a good home.
Check the Record Collector site for a price guideline and how to describe the condition of the items. Knock a couple of quid off what Record Collector say they're worth, then put any remaining items on Ebay or Amazon.
I wouldn't recommend trying to sell at a used record shop, simply because you'll get very little for them - they need to make a large mark up on items. For instance, you might be given 40p for a good condition 7" single, which they'll then price at a minimum of £3.
If you put together a list of what you've got, then post it on here in Buy/Sell/Trade at least people will get the chance to give you feedback as to what they think items would be worth and you'll get an idea of the level of interest.