Has this site been mentioned here before and I missed it? I was searching on the First Thrills anthology I have a story in that's coming out next month looking for reviews, and found this site instead. Apparently, not only does it track sales rank at Amazon.com, Amazon.ca, Amazon.uk etc. but also the actual number of sales.
Interesting! (Not that authors need something else to obsess over . . . )
Here's a sample: http://www.novelrank.com/title/first-thrills-hardcover