Some of the herbaria of the world:

Herbarium index

Geneva Herbarium

Royal Botanic Garden Edinburgh – Herbarium catalogue

Herbarium Catalogue – Kew Gardens

Harvard university herbarium

JACQ (jointly administered herbarium management system and specimen database

Natural History Museum – London

Sweden’s Virtual Herbarium
(Sweden’s six largest herbaria. 4.9 million specimens and 100,000 images)

Muséum national d’Histoire naturelle – Paris

Virtual Herbarium Berolinense – Berlin