What goes under your beauty blankie: what do you buy over and over?

I was just reading an interesting article in The Sunday Times Style yesterday about products that endure. They're iconic, top sellers. Because they work. And that's why people keep on buying them over and over. And in the end that's what really counts isn't it? Cos you can be conned into buying something crap because of a slick marketing campaign. But you'll only buy it once. What do you NEED: "like a child needs its blanket" (blugh hate that lyric, but anyway).

What would you have a knicker fit over if it was discontinued?
Which beauty products, in your opinion, deserve cult status?