Coleherne Court

A quarter of a million discount, but now in the zone where the stamp duty threshold comes into view.

http://www.rightmove.co.uk/property-for-sale/property-38043274.html?premiumA=true

Imperial Wharf

Imperial Wharf apartment with £300k slashed from the asking price.

http://www.rightmove.co.uk/property-for-sale/property-40489289.html

Horseshoe Lane, Totteridge

In many ways Totteridge beats Elmbridge if you like a balance of country life with good links to the city.  This place has had its asking price cut by half a million (sadly less than 10%).

http://www.rightmove.co.uk/property-for-sale/property-35889658.html

Hambledon Place, Dulwich

Out in not-so-prime London the drops can be dramatic.  30% off in two months.

http://www.rightmove.co.uk/property-for-sale/property-26103444.html

Addison Avenue, Holland Park

Compared to some apartments in the area, this almost looks like value.  Still Foxtons have had to slash the price...

http://www.rightmove.co.uk/property-for-sale/property-36019048.html

As a commenter pointed out, it's only a couple of blocks from some ugly tower blocks.  Addison Avenue is in the bottom right of this map.

More Prime Central London properties here. 

Wood Vale, Muswell Hill

A fallen through sale prompts a 15% reduction in the asking price of this semi in Muswell Hill.

http://www.rightmove.co.uk/property-for-sale/property-26103474.html