People search
These are generally of use almost entirely for the United States. I've included quite a few as the quality of results tends to vary - different ones are better for different searches, with no obvious consistency.
People-search tool for US
US public data search
People-search tool for US. Appears to give more info without login or sign-up than any of the comparable tools
People-search tool for US
People search website
Background check site. Emphasis on legal records. Free info very limited