Probably the most informative non-profit website on the Internet touching on all aspects of allergy. Although everything is not the same between how things are done in the UK and here there are surprisingly few differences. Just a great site.
General Allergy Sites
The Allergy and Asthma Network Mothers of Asthmatics
Americian Academy of Allergy, Asthma and Immunology AAAAI
American College of Allergy, Asthma and Immunology ACAAI
Food Allergy Sites
The Food Allergy and Anaphlyaxis Network