I have been using this great website called www.ipoints.co.uk for about a year now and I really really recommend you join up too.
Basically you get points for doing certain things like signing up to newsletters or filling in quick surveys.
Without much effort on my part I saved up enough points for a £30 Amazon vouvher which I have spent and am well on my way to getting another one soon.
It really isn't much hassle; infact just by signing up and claiming all of your 'free points' you can get enough points to receive two UCI cinema tickets.
Take a look if you think this may be for you.