May I recommend the Oxfam shop on Earl's Court Road. Picked up some fab bargains in there yesterday (dp got a beautiful Italian suit for £7 and I got a French Connection skirt for £2.75 and a cotton/linen Formes cardigan for £2.99). Items are not individually priced, eg all skirts are £2.75 and all suits are £7, so there are excellent bargains to be had.
Any other top tips for charity shops would be most welcome