Retailmenot is one but if you are a regular internet shopper, you may want to have a RSS feed of fatwallet forums where folks post deals. If you go to the website of your choice (except Amazon) through Fatwallet, you get certain % of your purchase back. For e.g. I made a purchase of $159 on JCPenny through them on Thanksgiving and I got $7 as a cashback. Yeah, looks small amount but I am willing to get every penny back that I can get.
Just to give you an example, through this forum, I got a Norelco shaver for $18, regularly priced at $49. Even head of my current Norelco costs $29.