Quidsin: This site is my favorite. Normal daily clicks can earn you 62p a day (£226 a year). However there are several offers where you can earn up to 30p by clicking and registering or entering competitions. If you have a few 'friends' with different e-mail addresses these offers can be signed up to several times a day. These can be found under the menu options of Cashback\Popular (e.g. TheRaffleClub, CCI and instantwin4now) and also Cashback\Quick Quids (e.g. 2 minute draw and beonscreen). Special offers come up all the time e.g The Guardian, Real Incentives, Tesco newsletters and Game Village. You can earn over £2 a day very easily, as long as you have several 'friends' with different e-mail addresses.
I have earned over £650 since last September with QuidsIn.
Quidco : There is no referral code here. This is the best site if you want to get cashback from purchases. But there is a £5 fee payable once a year. There aren't very many daily clicks but with Kelkoo, Hihgstreetweb and Carsource you can get about 34p a day easily (£120 a year). But the best thing is to get cashback on purchases such as insurance, do the same for your family and you can quite quickly earn £1,000 cashback.
rpoints : The best thing about this site is its user forums. If there is a misprice on the web they will tell you about it here. There are a few daily clicks available. You get to the recurring section by clicking on the work recurring near the top of the screen. At the moment you can get roughly 26p a day (£94 a year)
LoyaltyShopper : I haven't used this site for a while, mainly because I don't like the navigation around it. However I may go back soon as they have quite a few recurring points and other ways to make money. Could even be on par with QuidsIn for earning potential?
Cashbag: I haven't used this one for a while as I have been too busy with QuidsIn, but you can get 21p a day. It should only take a couple of minutes to get that. (£76 per year)
ipoints: Wasn't sure if I should put this one or not as it is pretty bad. No daily clicks normally and worse rates when purchasing things via links on their site. But you can earn some points from quick polls, webfetch searches and clicking through on e-mails. This one will take a long time to get anything. I think it takes me about 6 months to just get a £30 voucher, but then that is £30 more to spend.
wabbadabba: Not a cashback site. But if you earch the web using their page then every now and then someone wins a prize ranging from £5 or £10 amazon voucher to a plasma TV. (although no one has won a TV yet) I have won £15 with this since March.