International Union of Immunological Societies Allergen Nomenclature Sub-Committee.
The official list of Allergens maintained by The I.U.I.S Allergen Nomenclature Sub-commitee:
http://www.allergen.org

The Allergome Project.
A very useful and visionary database of allergenic molecules:
http://www.allergome.org

AllAllergy.
A portal to access a huge amount of Allergy resources on the web, including a digest of current articles in the field of Allergy and Intolerance:
http://allallergy.net