International Association of Accessibility Professionals (IAAP)
This is a summary of the 5 certifications they offer:
1. Certified Professional in Accessibility Core Competencies (CPACC)
General understanding of types and accessibilities and solutions in web and other settings. The CPACC is the ideal credential for those who manage and support accessibility, but who may not personally design, implement, or evaluate the technical details of accessible solutions.
Requirements:
1 year of experience in accessibility or a new/changing role with some responsibility for accessibility.
2. Web Accessibility Specialist (WAS)
for developers working and implementation accessibility principles and solutions. Requires minimum 3 years of working experience. The site lists study resources.