Manic Panic Atomic Turquoise Hair Dye
I absolutely love this colour. The amplified formula definately keeps it's freshly dyed brightness for longer than the normal one. I've never used any other brand so I don't have anything to compare it against but I still think it's pretty damn good! The whiter your hair is the brighter it'll be. Covering the dye (with cling film or shower cap etc) and heating with a hairdryer worked wonders for me too.