London may at the moment be one of the most expensive cities in the world if you are looking for trendy clothes. One of the cheaper options is the Portabello market.
However the main reason for going to Portabello is to experience the relaxed yet lively atmosphere. The Portabello Road is about 2 miles of smalls shops and people selling stuff directly on the street.
You can find antic furniture of a very high quality, clothes both new and second hand, CD's and a lot of different suveniers.
If you are in Notting Hill it would be a shame not to visit the Portabello market.