I sell on Amazon. the items have to be worth a lot of money, though because amazon takes out a commission for every little thing you sell.

Ebay Amazon.

Amazon, Ebay, etc. (Theres more but I only remember the ones I mentioned).

craiglist, ebay, amazon

kijiji ebay

www.ebay.co.uk

www.ebay.com (if you live in america)

or

www.amazon.co.uk

www.amazon.com (if you live in america)