I signed up with
TitleZ (titlez.com) back in 2005 and it is finally out of beta testing. It is free and kinda cool. Worth checking out.
My current favorite is
BooksandWriters.com which I think allows you to track one book for free for a while, but is super affordable. I currently pay a whopping ten bucks a year to track two of my books, and if I wanted to splurge and track ten books it would cost me a total of $20 a year (a year!!) How do they do it? Of course they have larger packages, but I don't need to spy on other authors.
What I like so much about BooksandWriters is that they are on top of it (hourly updates) and you can have emails sent to you daily or hourly (admittedly I used to check my ranking hourly, which can be fun when you are selling several books every day). Both services have charts and some kind of comparison thing. You really have to check them out and see what format you like.
. . . but I have just found a NEW site called
rankforest. I signed up for their free account, but it seems pretty limited. You really have to fork over ten bucks a month (every month!) or more to track books across the spectrum. I list them here because in all of the books I have read, only TitleZ is ever mentioned, so here you have three reliable services to track Amazon rankings for fun and profit.
If anyone has questions on the basics of Amazon ranking, try posting here. I have been watching my own books (okay, I used to spy on a few other authors as well) for a few years and I think I have a pretty good grasp on it. I am certain others have vastly more experience and knowledge as well, and they might be nice enough to share.