I'm not sure if this is really a deal - it's more information but it could save you money!
In the Marks and Spencer's sale I placed two orders which were both over £30 so qualified for their free delivery offer. Both orders were accepted with free delivery and the first part of my first order was dispatched as such. Then I was informed that some of the items I had ordered were out of stock. When I checked my account I noticed I had been charged £3.50 P+P on the rest of my first order and a further £3.50 on the 2nd order as some of those items were now out of stock.
I rang them to find out why and it seems that it happens automatically now if the value of your order goes below £30 BUT she said if I rang again once the orders had been completely dispatched they would credit the charges. I phoned again yesterday as I had received everything they had left, and sure enough the whole £7 was credited back to my account and I had email confirmations for all of the credits before I'd hung the phone up.
As orders placed in early January are still coming through I thought this was worth mentioning as you may not find out you'd been charged postage until you received the email saying your parcel has been sent.