Not sure if this has been posted before, had a quick look but couldn't find anything. If you go to http://www.whsmith.co.uk/privilegeclub
and sign up, they will send you an email with £20 worth of money off vouchers and then send you a further email each month with £10 of money off vouchers, which you can print off and use in store.
In the sign up email you get vouchers for...
£5 off when you spend £10 on any book
£5 off when you spend £20 (not entertainment)
£5 off when you spend £10 on kids books
£5 off when you spend £12 on stationery and cards
(These expire on 31st December)