According to the Transport for London web site:

Barclays Cycle Hire, launching on 30 July, will be a public bicycle sharing scheme for short journeys in and around central London.

You’ll be able to pick up a bicycle, use it as you like, then drop it off at one of 400 locations in central London, ready for the next person.

I took this photo today of a series of newly installed cycle rack was taken outside Loewy’s office on Bankside.