We recommend the following newspapers/magazines:

EVENING STANDARD: This 'London' newspaper of 'London' contains a useful Classified section. The first edition is available at around 10am.
Cost: 40p    When: Monday to Friday
Where to buy: newsagents and outside Underground/train stations

TNT Magazine: This well known free magazine is aimed specifically at the young foreign community in London contains a large classified advertisement section.
Cost: Free    When: Monday
Where to find: outside Underground and train stations (in metal containers)

LOOT: This newspaper offers thousands of classified advertisments organised under many headings.
Cost: £1.40    When: Monday to Saturday
Where to find: all newsagents and many shops

ICI LONDRES: This monthly magazine is specifically aimed at the French community in London. It contains a useful classified advertisment section.
Cost: Free  When: Monthly (at start of month)
Where to find: in shops in 'French' areas such as South Kensington