How can you date someone who you're already friends with?

Alright, there’s this girl I’ve been into for a long time. When we met she was involved with somebody, but she was friends with all of my friends so we inevitably started spending time together. She has since become single, and it’s been long enough that the ‘rebound’ phase has passed, but now I have a different problem. How can I get her to think of me as more than a friend? I know that if I were to just ask her out I would get a ‘let’s just be friends’ at this point because that’s where our relationship is at this moment.

What can I do to escape the shackles of friendship and take it up a notch?