There are many websites that contain useful background information on the topic of genetic modification and the current debate.

• A good place to start is the Bioethics Briefing on Crop Plant Genetic Modification which covers the technology involved as well as the ethical considerations. 
• The Nuffield Council on Bioethics are an independent body who examine and report on the ethical issues within biology and medicine. A past project on GM crops published a report in 1999 titled ‘Genetically modified crops: the ethical and social issues’
• The NCBE have an extremely useful guide to GM food which covers the technology, issues, regulations, case studies, history and links to other sites and publications.
• New Scientist magazine has a website with an introduction to genetic modification and the latest news articles.
• The Soil Association promote plant-friendly food and as such campaign against GM food.
• The Food Standards Agency is an independent Government department who protect the public in relation to food. Their website provides information on their work such as safety assessments and also provides a few teaching tools. 
• Greenpeace – a charity that campaigns against GM food.