OCLC Online Computer Library Center: http://www.oclc.org/home/
OCLC WorldCat: http://www.oclc.org/worldcat/
Office of the Commissioner of Official Languages (Canada): http://www.ocol-clo.gc.ca/
Office québécois de la langue française (OQLF): http://www.oqlf.gouv.qc.ca/
OneLook Dictionary Search: http://www.onelook.com/
Online Books Page (The): http://digital.library.upenn.edu/books/
Online Originals: http://www.onlineoriginals.com/
Open eBook (OeB) Forum: http://www.openebook.org/
Opera: http://www.opera.com/
Organisation de coopération et de développement économiques (OCDE): http://www.oecd.org/