I've been tweaking isbn.nu, my comparison service that finds the prices for a given book via online bookstores, for days, and I have some neat new offerings that are subtle, but useful.Among other elements I've added is a list of books that Amazon.com says other people who bought a given ISBN also purchased (when available for a title), which appears in the blue bibliographic box below the price comparison. I also finally completed the first stage of a long-envisioned project to add "authority" to the system so that multiple books by the same author would show up as editions of a single work. This is now working for author and title searches. It also shows up as Other Editions below a price comparison list of prices for individual titles. Feedback, anyone? I'm hoping to make my service more and more useful for people trying to find specific books and editions.