The John Frieda sheer blonde range are great. They are not cheap but at the end of the day you get what you pay for! I use them all the time. They also do lots of different hair treatments as well. Good luck x
I use Toni & Guy Violet colour shampoo. You get it from the salon - not the one in Boots. They'll mix it for you there and then. It isn't cheap (�7 for a small bottle - �13 for large) but it is by far and away the best one i've ever used. It gets rid of all the brassy / yellow tones.