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/