my favorites:
"is your name visa? because you're everywhere i want to be."
"you must be a librarian-you just increased my circulation."
and for one that actually works:
"i've had a really bad day, and those always get better when i see a pretty girl smile. will you smile for me?"
or, in the case of bicurious college girls:
"i'm a lesbian." (seriously, that's all it takes.)