N.U.S - National Union of Students
StudentCents - you can't miss these guys, they were the ones who most likely supplied you with your fresher's pack!
Newspapers:
Times student vouchers - requires registration
Other:
3 driving lessons for the price of 2! - AA driving school
Valued opinions - complete surveys and get paid in vouchers (you chose which vouchers you want at when you register). After registering, you are invited by email to each survey. You may not qualify for all surveys. Takes a while to accumulate a reward.
Opinionpanel Research - like Valued Opinions, only less frequent! Rewards only in Amazon vouchers.