Textract.com is a semi-automatic indexer. It is really easy to use and provides you an editable list of words and ideas along with the page numbers they appear on. It's much better than trying to manually index and it was much more comprehensive than the list we came up with. It still takes some time but no where near the time of doing it manually.
FAQs can be found here http://www.texyz.com/textract/faq.htm
I have personally used this software to create a back-of-the-book index.