I can't be doing with the crush of the start of the sales - DH and I both do the same, wait until the tail end of the sales and then see what's left at rock-bottom price. Bought some gorgeous "hooker boots" in M&S a couple of years back for £20 down from £100 - last pair left, black satin pointy stiletto ankle boots, v sexy with nice jeans. (Or with nothing...)
I keep tags on anything I don't need to wear, then if it goes in the sale I buy it and take back the full price one. Beware shops have no legal obligation to refund something just 'cos you don't want it, so check out the returns policy first (eg within 28 days), and also you would have to secure one in your size, then take back the other - they wouldn't just give you a refund and let you buy it, most shops would give you the refund then say that you have to take your chance when it goes back on the shop floor.
As due to drop sprog any day now, haven't gone to the shops, but bought loads for kids on Next/Boden/Marks sales (bought 3 sets girl/3 sets boy stuff in Next as will have had sprog before returns date passes!) Also got less-than-half-price McLaren buggy from Next for summer hols (only suitable for a girl as pink though!), and some half price unisex cot bedding.
Worst buy - high heeled beaded strappy shoes with those criss-cross ties that do up like ballet shoes - they were only £5 down from £45 but they are so bloody awkward to wear, and if you walk anywhere the ties start to undo. As I have large feet (size 8), perhaps I should sell them to a cross-dresser on eBay