Marxist references
http://www.marxists.org/
http://www.marxists.org/archive/lenin/
http://www.marxists.org/archive/trotsky/
http://www.marxists.org/archive/luxembur/

News
http://www.alternativenews.org/
http://electronicintifada.net/new.html
http://al-awda.org/
http://news.bbc.co.uk/
http://www.michaelmoore.com/
http://indymedia.org/
http://english.aljazeera.net/HomePage - The site they tried to ban!

http://www.esf-democracy.org

Trade union labour movements
http://www.labourstart.org/
http://www.labornet.org/

Gay rights
http://www.stonewall.org.uk/stonewall/

Political prisoners
http://www.mumiabook.com/

http://www.freemario.org

Activism
http://www.zmag.org/ - Thorough and comprehensive website with more information than you can shake a stick at.
http://www.urban75.com - Infamous activists website!
http://www.palsolidarity.org/ - ISM website
http://www.corporatewatch.org/ - Does exactly what it says!

Left wing organisations

http://www.fifthinternational.org
http://www.workerspower.com
http://www.socialistparty.org.uk/
http://www.swp.org.uk/
http://www.actionforsolidarity.org.uk/