What are they like? How long are they?

I like the little (2", 5cm) black hairpins they sell everywhere. I bought some larger hairpins, which are stronger, but the ends aren't rounded, so you have to be really careful with them.

I got some hairpins I really like from a dance studio. They're sold by Bunheads http://www.bunheads.com/, nice and strong, curved like the head, in sizes of 2-1/2" and 3".