Apart from camelcamelcamel, there's also Invisible Hand [1] for Firefox, Chrome and Safari that provides price comparison and updates. I doubt if it can avoid browser sniffing or fingerprinting though. Also, it works only in the U.S., the UK and Germany and it makes money from commissions paid by some retailers.

Any kind of comparison is better than no comparison at all. :)

[1]: http://www.getinvisiblehand.com/

This is mentioned by someone else on the top as well. I love camelcamelcamel and it's chrome browser extension. You can limit it to be able to run only when you are on amazon domain.