I think the brightest lip product I own is a Sleek Pout Paint, but a) I don't like the way it looks alone so I'd only wear it mixed with other colours and b) it's not a lipstick.
The brightest lipstick I own is Revlon Cherries in the Snow. I'll take this opportunity to speak out about a certain fact regarding Cherries in the Snow, inspired by Charlotte at Lipglossiping: It is not red.
That's right. Revlon 'Cherries in the Snow' is not red. Despite what magazines and some other blogs may tell you, it is not red. 'Cherries in the Snow' is pink. Really pink. Not even red-pink. Definitely pink.
And quite a bright pink at that. Before I got my own tube, I was under the impression that it was red. I was expecting it to be red. Then I put it on, and BAM. Hello, unexpected pink. Even with reddish-pink lipliner underneath, it still definitely pulls pink.
Despite the unexpected colour, I really like this lipstick. It lasts very well and doesn't go patchy like some lipsticks do.