What’s your favorite way of getting Web-site traffic data? I’m looking for something reliable and, if not free, then at least incredibly cheap.

I’ve played with Quantcast and Compete.com. Quantcast is supposedly more reliable, but only if the site owner registers, or “Quantifies.”

Nielsen and comScore are paid services.

Does Google offer anything? It doesn’t seem to, but maybe I’m just looking in the wrong place.

Clarification: Sorry. I see from the comments I’m getting that I did a poor job of explaining what I’m looking for. I want data on other people’s Web sites, not mine.