http://threering.net:3/
It's safe, fast and painless, no advertising, no nonsense. All it does is try to guess where you are.
I got 92% likely to be in Philadelphia. I'm not exactly, so it's wrong. But it's *interestingly* close; my ISP is in Wilmington, but has a Philly office, and my connection routes through that office.
And the map it paints is pretty sparse right now... which is why I pass the link along. How'd it do for you?