I've tried quite a few cashback sites, reluctantly at first as I didn't like the look of most of them. But I persevered, and I have to say that my favourite so far is www.giveortake.com, which strangely doesn't seem to have been mentioned here! They give you cashback on Amazon which the others don't and I do most of my shopping there. but also you get 100% cashback on everything (rather than only half which most cashback sites give)and the design is really nice.