English Index: This gives English and scientific names for all spices. This is basically the type of index you would expect to find in a printed book, and is recommended for a first search.
Alphabetic Index: This very large index contains spice names in more than 50 different languages, alltogether approximately 10000 keywords. Names from languages using a non-Latin alphabet are romanized; often, I use different romanizations for the same native word to account for variation in other literature.
Botanic Index: This index is organized according to botanical taxonomy. Spices are grouped into families, orders, ...
Morphologic Index: Here, spices are sorted according to the plant part used in cooking. This indes ist particularly useful if you want to identify a stange plant product found in a place where you do not speak the local language.
Geographic Index: This index lists spices by regions. For each region, native spices and thos spices much used in contemporary cuisines are listed, and local culinary traditions are reviewed shortly.
Spice Mixture Index: This index lists spice mixtures from all over the world and mentions some of their main ingredients.

There are also many indices that allow to identify a spice starting with its name in a foreign language.