I think I might have mentioned this before, but use Amazon's Marketplace.
Your listing will stay up for 6 months - with Ebay it's only 10 days at the most.
Just look-up the item you want to sell on
http://www.amazon.co.uk , then click 'Sell Yours Here'.
Amazon take a cut (about 20%) but you'll do much better than on Ebay or local second-hand shops.
The money gets paid straight into your bank account, and Amazon will send you an email saying where to post it to. It's much less hassle than Ebay.