British Newspapers online - The British Library
At the moment (January 2009) only four English newspapers archives are freely available online through the British Library for few days/weeks/months/years only. These are: Manchester Guardian (1851, 1856, 1886) - Daily News (1851, 1856, 1886, 1900, 1918) - News of the World (1851, 1856, 1886, 1900, 1918) - Weekly Dispatch (1851, 1856, 1886, 1900, 1918).
The JISC British newspapers digitisation programme for 1620-1900 is not available freely outside the United Kingdom (see http://www.jisc.ac.uk/whatwedo/programmes/digitisation/newspapers2.aspx )