Our open-date site has links to about 600 useful datasets from US and Canadian government and a handful from the UN. The US federal government datasets are sorted by department.
http://www.opengeocode.org/cude1.1/index.php
We [opengeocode.org] maintain a catalog of open data portals across the world. We've categorized them under the categories:
- Data Portal (multi-category)
- Transparency Portal (budget, payroll, expenditures, etc)
- GIS/Gazetteer (maps, geolocation data, etc)
- Census/Demographics
- Health
- Education
http://www.opengeocode.org/opendata/