Where can I learn more about professional certification?

One of the best sources of information about professional certificates is the Department of Labor's Career Onestop Certification Finder database, accessible at http://www.careeronestop.org/EducationTraining/Find/certification-finder.aspx.  Though this website is funded by the US government, many of the credentials it lists are internationally recognized, and all certificates are vetted to some degree to ensure that they meet some basic level of recognition.  While there are a few certificates that I was not able to find in a recent search of the database - for example, the Yoga Alliance and Federation of Dining Room Professionals seem to be conspicuously absent - it remains probably the world's best source of objective information about occupational and professional certification.  In perhaps a wise political move, the US Department of Labor and its contractors avoid endorsing specific certifications or offering any sort of reviews that compare different certification options, though most of the information on the website at least seems to be accurate.  Searching the database by occupation is a great starting point as you look for more information about certification options!