While I like to use the "You look like you're having the most fun here" line on occasion, I'm really just using it to get out of the door. I then will bounce off to something else, ask her what she's up to, if she's with friends, what she's drinking, whatever I feel like after that. The key to having good, long, natural conversation is exactly that. Yes, you can have canned openers and routines and all that stuff but ultimately, if you can just go up and have a conversation with her, while being fun and having some idea of where you want to steer the conversation, you can talk to a girl for a pretty long time. That being said, if she's not biting, it doesn't matter what your canned lines are or your natural conversation, women will just shut you down if they aren't interested. If you sense they're not interested, bounce off to another girl and move on with your night.
A good piece of reference for this is this Real Social Dynamics Video:
A good piece of reference for this is this Real Social Dynamics Video: