I recently used this site to buy the Essie Fall Mini Collection and thought the service was pretty good. Their prices are very reasonable on certain brands and an extra 10% off is always good! They sell everything from haircare and skincare to cosmetics and nail polish.
UK shipping is totally free as well - I love that! I don't know why I always begrudge paying shipping. Probably because when I order a lipstick which would cost less than £1 to ship, I have to pay £3-4 instead!
Anyway, if you're interested, check out their site here!
Happy shopping :)