If I were a boy, I'd have hair like this

Shorter on the sides and longer on top.
This look is really popular this year and I'm in love with it. It's classy, sexy and versatile; it can be styled in a number of different ways to achieve different looks. There's the slicked back undercut, Brit rock-indie, rockabilly, and quiff.
My favourite is the textured messy quiff.

Here's a good site with some more info and explanations.