Damn, MasonM stole my sure-fire line. Experience has taught me that a pretty woman, standing by herself at a bar, is either waiting for someone and does not want to be hit on, is by herself because of some serious unseen flaws or is waiting for her huge, professional football-player boyfriend to return from the bathroom.
If she is none of these, then 'Hi, isn't it nice how places like this allow total strangers to meet each other and become friends' is a line that has worked for me. It is not overly funny or sleazy and usually, at the very least, illicits a polite response.
