Buildings data from Allegheny County, Pennsylvania via PASDA
Data Citation

Buildings data from the City of Austin, Texas via their GIS FTP site set up by the Communications and Technology Department.
A data disclaimer is written on the GIS FTP site.

Buildings data from the City of Baltimore, Maryland via the Mayor's Office of Information Technology
Released into Public Domain

Buildings data from the City of Bloomington, Indiana via their website.Source
Data Policy

Buildings data for the City of Boston via the Boston Redevelopment Authority
Data Policy

Buildings data from the Town of Chapel Hill, North Carolina via their website, TownOfChapelHill.org
GIS Data Disclaimer

Buildings data from the City of Chicago via data.cityofchicago.org
Public Data

Buildings data from Clark County, Ohio via Digital Data Technologies, Inc.

Buildings data from Honolulu Land Information System (Holis), Department of Planning and Permitting, City and County of Honolulu.
Data Download Page

Buildings data from Kitsap County, Washington via their GIS portal.
Data Policy

Buildings data from Lancaster County, Pennsylvania via PASDA
Data Use Policy

Buildings data from the City of Midland, Texas via MidlandTexas.gov
GIS Data Information Page

Buildings data from Nanaimo, British Columbia, Canada. Available under a Creative Commons Attribution 2.5 license.

Lots data from NYC PLUTO

Buildings data from the City of Oakland via Broadway/Valdez District Specific Plan

Buildings data from the City of Petaluma, California (and multiple online sources, not necessarily controlled by the City of Petaluma) via CityOfPetaluma.net
GIS Data Information Page

Buildings data from the City of Philadelphia via OpenDataPhilly.org
Data Use Policy

Buildings data for the City of Raleigh, North Carolina via Wake County's GIS page
Data Disclaimer

Buildings data from the City of Round Rock, Texas or its agents via RoundRockTexas.gov
GIS Data Information Page

Buildings data from the City and County of San Francisco, California via data.sfgov.org
Creative Commons Zero License

Buildings data from the Metropolitan Planning Commission and Savannah Area GIS. Visit thempc.org and SAGIS.org
Data Use Policy

Buildings data from the City of Seattle via data.seattle.gov
Public Domain

Buildings data from the City of Spokane via their GIS portal.
Data Disclaimer

Buildings data from the City of Steamboat Springs, Colorado via their GIS Page

Buildings data from the City of West Sacramento, California via their GIS site
Data Disclaimer (PDF)