As a member of the American Society of Indexers (ASI), I have to put in a plug for the word "indexes."
This is the preferred spelling in most dictionaries for the lists of terms with locators that are found, ususally, in the backs of books. ASI also promotes the use of "indexes" as the plural of "index." Likewise for appendix/appendixes. "Indices" is used by financial and meteorlogical folks. I don't remember who uses "appendices" except my colleagues who are thoroughly familiar with church Latin.
