I recently clocked on to the fact that you could convert your Tesco clubcard vouchers in to double there worth at beautyexpert.co.uk which meant that I could finally use my stash of vouchers lying in a draw. They do OPI and Essie polishes along with lots of other beauty bits and bobs.
(OPI - My Private Jet)
The whole transaction went smoothly and the package turned up the next day. My only complaint was the amount of packaging a huge box full of that starch polystyrene. A nice bonus was the two free sachets of moisturiser I got, although one is for men so have had to pass that on.
Also if you go to beautyexpert.co.uk via topcashback (if you'd like to sign up with my referral code you can if not that's fine, its a really good site regardless) then you get paid a percentage of the total in cash back.
Not quite free but still worth a mention!
[FYI not affiliated with any of the companies, just thought I'd share the experience]