Came across a POF profile and couldn't remember if I had opened her before or not (turns out I hadn't). Rather than risking sending a 2nd opening message, I went for something a little different:
Me: So, you're pretty cute...why haven't we gone out yet?
Her: awe thank you

I dont know guess cause you have yet to ask a girl out mister.
Me: Hmm, you know, that makes sense! I should probably start by asking for your number. I'm T, by the way.
Her: Nice to meet you T. XXX-XXX-XXXX - *NAME*
She's about a 7, and I doubt it would work on anyone higher than that, but I was definitely surprised at how little effort this one took!