A lot of people use "people" search engines and Google dorks to find people or information about people, but you can actually find out quite a bit of information via public registries. Consider some of these:
The Knot - Wedding Registry Search
RegistryFinder - Baby Shows and Graduation Search
MyRegistry - Wedding, Baby, and Gift List Search
Amazon - Registries for Any Occasion Search
Bed, Bath, and Beyond - Gift Registry Search
The Bump - Baby Registry Search
You can also find out PII of anyone in the United States who is registered to vote, by looking at local election registries. Does anyone know other registries to include?