London is a shoppers paradise, there are thousands of shops and stalls, everywhere, far too many perhaps.
Oxford Street
Oxford street is definitely London's and probably England's and Britain's premiere shopping street. Unfortunately though it not a particularly pleasant experience. It is busy, very busy, dirty, and a jumble of extremes from Selfridges to Mr Buyrite. Perhaps its most lauded venues are the afore mentioned Selfridges, John Lewis, the biggest BHS, a giant Topshop / Topman, a large HMV, a mega Virgin Mega Store, Marks and Spencer, House of Frazer and more. The shops are mostly big names and a few legendary department stores. I would suggest shopping before midday to make it more tolerable.
Camden Market
Camden market remains London's most famous market. It is rapidly changing but has retained its charm. Though there is perhaps less in the way of second hand clothing here now, it can be find in the Stables. Worth a visit but don't expect too much, though you may still spy the occasional punk and doubtless a good number of goths.
High Street Kensington
Very slight more upmarket than Oxford Street, not anywhere near as big, and not quite as busy. There area good number of out doors shops here, Blacks, North Face, Millets etc. Then some high streets staples such as H&M (unusually with a men's section),
Zara, M&S, Gap (erk) and more.