If you want a long lasting colour, do not use products such as Manic Panic, as they aren't permanent. I personally use Scruples Urban Shock Colour Craze, which is a product you can only buy at salons, it lasts me a good 2 months, but only comes in seven colour, which are very vibrant, and can be turned into pastels. I have friends who use Special Effects or SPLAT, but I don't know much about them! They don't last as long as Scruples, but they are nice too.